In a recent game our Rogue (level 9) attempted to tumble past a Greater Water elemental (CMD 40) and failed. After the session he looked up his opponents CMD and realized that he would have had to roll a natural 20 just to make the check (Acrobatics Skill bonus was 21).
He and I are little bit confused as to why it's easier to tumble past a smaller, dexterous opponent vs. a huge, lumbering elemental.
Why is Str including in the CMD against tumbling at all? Attacks rolls, grappling and overrun I can understand… but why tumbling?
Has anyone else run into this problem?
In a recent game our Rogue (level 9) attempted to tumble past a Greater Water elemental (CMD 40) and failed. After the session he looked up his opponents CMD and realized that he would have had to roll a natural 20 just to make the check (Acrobatics Skill bonus was 21).
He and I are little bit confused as to why it's easier to tumble past a smaller, dexterous opponent vs. a huge, lumbering elemental.
Why is Str including in the CMD against tumbling at all? Attacks rolls, grappling and overrun I can understand… but why tumbling?
Has anyone else run into this problem?
Without referring to the description of the elemental I would guess that a CMD of 40 would suggest that it may not be all that "lumbering", or that maybe it is just that big and strong. And tumbling past a smaller opponent can be easier simply by virtue of being able to jump over them. Strength is quite easily applicable to a check against tumbling because it would influence how cleanly you must evade their attempts to lay hands on you. A tiny rogue with a Str of 7 might be able to get both arms around you but not be strong enough to keep you from slipping through anyway; whereas a hulking barbarian with a Str of 22 might only get a partial grip with a single hand on you but have the sheer power to stop you in your tracks with just that.
That being said, I've always found it curious that both dex and str count for CMD, but only str counts for CMB (absent special feat/abilities).
That being said, I think the CMD of a greater water elemental should be 39 not 40
In a recent game our Rogue (level 9) attempted to tumble past a Greater Water elemental (CMD 40) and failed. After the session he looked up his opponents CMD and realized that he would have had to roll a natural 20 just to make the check (Acrobatics Skill bonus was 21).
He and I are little bit confused as to why it's easier to tumble past a smaller, dexterous opponent vs. a huge, lumbering elemental.
Why is Str including in the CMD against tumbling at all? Attacks rolls, grappling and overrun I can understand… but why tumbling?
Has anyone else run into this problem?
Without referring to the description of the elemental I would guess that a CMD of 40 would suggest that it may not be all that "lumbering", or that maybe it is just that big and strong. And tumbling past a smaller opponent can be easier simply by virtue of being able to jump over them. Strength is quite easily applicable to a check against tumbling because it would influence how cleanly you must evade their attempts to lay hands on you. A tiny rogue with a Str of 7 might be able to get both arms around you but not be strong enough to keep you from slipping through anyway; whereas a hulking barbarian with a Str of 22 might only get a partial grip with a single hand on you but have the sheer power to stop you in your tracks with just that.
That being said, I've always found it curious that both dex and str count for CMD, but only str counts for CMB (absent special feat/abilities).
I disagree. Size is already factored into the CMD (10 + Str.Mod + Dex.Mod + Size.Mod). First off, we are not talking about Grappling,
we are talking about evading. Why should my opponent's STR apply tomy evading him, if he can't even lay a hand on me?
Secondly, the STR will come into play if the Rogue fails the Acrobatics
DC check. The opponents STR will factor into his/her Attack of Opportunity to hit score.
I propose that the Acrobatics DC should be:
10 + Dex.Mod + Int.Mod + Size.Mod (Substituting Int for Str)
Maybe you could add a few pluses if the opponent has Combat Reflexes.
As a president, Bluff does not use CMD, but has its own DC calculation
based on Wis.Mod or Sense Motive.
DC = Max(10 + BAB + Wis.Mod, 10 + Sense Motive)
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To end my reply, think about this classic Fantasy situation...
A spry, nimble, hobbit is fighting against a huge lumbering Giant..
In the story the hobbit jumps nimbly through the Giant's legs,
narrowly avoiding his huge (strong?) hands.
How would you simulate this if the hobbit needed an Acrobatics of >30 to
have a chance to tumble past a CMD 40+ creature?
Why should my opponent's STR apply to
my evading him, if he can't even lay a hand on me?
Because evasion is not simply an all or nothing proposition. Evading someone's attempt to stop you does not mean they did not even lay a hand on you. If you are familiar with American football, you could think of an armtackling situation: it's easier to avoid a slightly quicker but much smaller guy because all you have to do is keep him from getting a solid hit on you with his weight and momentum behind it; but a much bigger and slightly slower guy is a tougher proposition because then you must actually keep him from even laying a hand on you.
And being bigger and less dextrous does not necessarily mean that they are immobile statues. As was pointed out earlier, the water elemental in question has combat levels and the ability to maneuver. That it also has a significant strength advantage just makes its maneuvers more difficult to overcome.
A spry, nimble, hobbit is fighting against a huge lumbering Giant..
In the story the hobbit jumps nimbly through the Giant's legs,
narrowly avoiding his huge (strong?) hands.How would you simulate this if the hobbit needed an Acrobatics of >30 to
have a chance to tumble past a CMD 40+ creature?
Wouldn't the Giant be 3 sizes larger, enabling the hobbit to move through the space unhindered (unless you are complaining about the general proposition of attacks of opportunity)?
Why should my opponent's STR apply to
my evading him, if he can't even lay a hand on me?Because evasion is not simply an all or nothing proposition. Evading someone's attempt to stop you does not mean they did not even lay a hand on you. If you are familiar with American football, you could think of an armtackling situation: it's easier to avoid a slightly quicker but much smaller guy because all you have to do is keep him from getting a solid hit on you with his weight and momentum behind it; but a much bigger and slightly slower guy is a tougher proposition because then you must actually keep him from even laying a hand on you.
And being bigger and less dextrous does not necessarily mean that they are immobile statues. As was pointed out earlier, the water elemental in question has combat levels and the ability to maneuver. That it also has a significant strength advantage just makes its maneuvers more difficult to overcome.
Let's take your American Football example...
A very fast dexterous Corner-back can totally avoid the big Offensive
Tackle by running around him, or executing a swim move, or a spin move.
He at least has a chance of avoiding the Tackle's strength.
Wouldn't the Giant be 3 sizes larger, enabling the hobbit to move through the space unhindered (unless you are complaining about the general proposition of attacks of opportunity)?A spry, nimble, hobbit is fighting against a huge lumbering Giant..
In the story the hobbit jumps nimbly through the Giant's legs,
narrowly avoiding his huge (strong?) hands.How would you simulate this if the hobbit needed an Acrobatics of >30 to
have a chance to tumble past a CMD 40+ creature?
We are talking about **threatened** squares. The Att. of Opp. is
invoked whenever you leave any threatened square.
I disagree.
The elemental must first out-maneuver the rogue; I do not see how Str comes into play here.
The attack roll bonus from Str I can understand - but not when it's applied to CMD vs. tumbling. If you're trying to out-maneuver someone their size should also be applied as a disadvantage - not a benefit.
After all, when was the last time a body-builder caught a fly in mid-air?
A very fast dexterous Corner-back can totally avoid the big Offensive
Tackle by running around him, or executing a swim move, or a spin move.
He at least has a chance of avoiding the Tackle's strength.
Yes, but (speaking from direct experience) that is easier to do against a weaker tackle than it is against a stronger tackle. Against a weaker tackle, if you slip by him and he just gets a hand slap on your shoulder, your progress is essentially unimpeded. If you have the same result against a stronger tackle, his hand slap on your shoulder will more significantly imped your progress, potentially stopping you altogether (if he's strong enough). When you're talking about superhuman beings (like greater water elementals and giants) instead of people, then a mere finger might be enough to stop a tumbling hobbit.
We are talking about **threatened** squares. The Att. of Opp. is
invoked whenever you leave any threatened square.
Ah, so you are objecting to the general rule of the attacks of opportunity. My bad. I thought you were objecting to the ability of the opponent to stop you from getting through the square.
In terms of the AoO, the Str would factor into their ability to launch that attack in the same sense that it would add to their ability to hit with it.
If that weren't the case, wouldn't a simple acrobatics check be sufficient to nullify any attempt at attacking?
Yes, but (speaking from direct experience) that is easier to do against a weaker tackle than it is against a stronger tackle. Against a weaker tackle, if you slip by him and he just gets a hand slap on your shoulder, your progress is essentially unimpeded. If you have the same result against a stronger tackle, his hand slap on your shoulder will more significantly imped your progress, potentially stopping you altogether (if he's strong enough). When you're talking about superhuman beings (like greater water elementals and giants) instead of people, then a mere finger might be enough to stop a tumbling hobbit.A very fast dexterous Corner-back can totally avoid the big Offensive
Tackle by running around him, or executing a swim move, or a spin move.
He at least has a chance of avoiding the Tackle's strength.
But we're talking about Acrobatics/Tumbling here. The point
is to avoid him/her, completely! Slip past his/her grip.Use the Rogue's Dex as a counter to the Giant's Str.
After all, when was the last time a body-builder caught a fly in mid-air?
When was the last time you saw Mary Lou Retton get through a doorway Andre the Giant was trying to block?
But we're talking about Acrobatics/Tumbling here. The point
is to avoid him/her, completely!
And that is MUCH harder than simply getting past someone without them getting a chance to get a swing in on you.
Consider this: to avoid the attack of opportunity would mean that at no time in the movement are you within the swingable motion of the weapon. Now, if someone is strong enough to swing their weapon quickly in any direction, the area you must avoid to deny them even the possiblity of attacking you is much greater. If someone lacks the strength the get a meaningful blow all the way around quickly enough, then it is easier to find a gap where they can't swing at you.
Slip past his/her grip.
Again, if you are talking about getting past the person rather than avoiding the attack of opportunity, then slipping past their grip requires FAR more acrobatic movements than simply moving in such a way that they cannot get a solid grip on you. The less grip they need to stop you, the more completely you need to avoid their grip altogether.
Or would you consider (reversing the situation) a hobbit almost certain to stop the giant because the giant can't avoid his grip?
Use the Rogue's Dex as a counter to the Giant's Str.
That's exactly what it is doing; which is why the giant's str is a factor that has to be countered. Otherwise the hobbit would be trying to counter the giant's str with his own str; hardly a favorable proposition.
There is a reason why Offensive Linemen are big guys...
And Defensive Linemen aren't hobbits . . .
Could make a nice, be is situational feat;
Duck & Run,
Gain +4 on Tumble checks for every Size Category your opponent exceeds you.
Your Medium Rogue would get +8 on its check. Although I like the flavor, it's probably way to situational. I'd love to see a bunch of Tiny critters run amok with this amongst a party though.
When was the last time you saw Mary Lou Retton get through a doorway Andre the Giant was trying to block?After all, when was the last time a body-builder caught a fly in mid-air?
What about an open room? Your analogy describes tumbling through an opponent’s square (which is much more difficult for a reason). That's not the situation I brought up originally.
What about an open room? Your analogy describes tumbling through an opponent’s square (which is much more difficult for a reason). That's not the situation I brought up originally.
Maybe have the Str.Mod apply if trying to move through an occupied square.
That's not the situation I brought up originally.
Then I apologize; I completely misread your post.
However, I think the rational can still be applicable (though certainly less so). The stronger an opponent is, the more freely and quickly they can swing their weapon (or other attack). Thus, they can effectively strike at a higher proportion of the threatened square making it more difficult for an acrobat to tumble precisely through the areas of the 5'x5' square where the opponent cannot physically bring the attack to bear (which is what it means to avoid the Attack of Opportunity).
Basically, I think the idea is that strength makes you better in combat; that's why it gives a bonus to hit as well as damage. Obviously, skill, dexterity, size and other features are also going to factor in, but I think strength is a reasonable factor as well.
That's not the situation I brought up originally.Basically, I think the idea is that strength makes you better in combat; that's why it gives a bonus to hit as well as damage. Obviously, skill, dexterity, size and other features are also going to factor in, but I think strength is a reasonable factor as well.
No need to apologize.
I agree that strength helps you hit more effectively, that's why I'm not questioning the mods to an attack role.
I feel that the opportunity to make the attack should not be influenced by STR, but instead by Dex. After all, spring attack allows you to completely ignore attacks of opportunity, regardless of how strong the opponent is. Acrobatics should be not be orders of magnitude more difficult especially against opponents of an appropriate CR.
After all, in my original example (which occurred at the gaming table) the Rogue had MAX'd his acrobatics skill and even had magical enhancements.
I feel that the opportunity to make the attack should not be influenced by STR, but instead by Dex.
I see your point. But the way I look at it, the ability to attempt an attack of opportunity is a reflection of one's competence with that melee attack. Strength enhances that competence, as expressed through the bonus on to hit rolls. That enhancement reflects the ability to more comfortably control the weapon in your grip, the ability to swing it more rapidly (thus making it more likely for the target to still be where you are swinging), the ability to adjust swings and maneuvers in progress through sheer force (think of a sword swing that misses but the guy is strong enough to reverse stroke immediately before the target can adjust; that's not hard to envision is the course of a six-second round of fighting), and other related factors. Those factors would also come into play when determining whether someone is able to avoid your attack of opportunity. Just like acrobatics cannot automatically negate a strength bonus on regular attacks, it is not necessarily able to negate the impact of strength on an opponent's ability to attempt an attack of opportunity.
That's the way I see it, anyway.
As for the difficulty, I noticed that the Greater Water Elemental has the second highest CMD of any CR9 creature (second only to the Greater Fire Elemental) and (by my count) some 5 points higher than the normal calculation. That would strongly suggest to me that this particular creature is particularly adept at countering combat maneuvers of all types. So I don't really see it as a problem that there is some creature out there at the appropriate CR that can counter this rogue's acrobatic talents in this one particular manner, even though they are maxed out. To me, it would be comparable to creature with a spell resistance high enough that spells from equivalent level casters would be nearly useless; some creatures just demand an alternate approach.
Also, since it has both the Lightning Reflexes and Dodge feats, plus a dex of 20, I don't think "lumbering" is a very apt descriptor.
On a not-quite-related note, I still don't get why Dex is not a part of CMB, though.
Including Str Bonus in CMD makes sense in many cases, but it's not very logical in this case, the DM just needs to make a call.Don't forget the most important rule :)
Yeah, I should mention that I probably wouldn't go with the RAW in this case, either. I'm just pointing out how the RAW can make sense.
I'm not sure exactly how I'd fix it, but it would probably involve a combination of the rogue's CMB and Acrobatics. Although it would be dicey; anything giving the rogue a reasonable chance against the second most powerful anti-Combat Maneuver creature at that CR would make the rogue essentially unhittable by normal foes. And I do not read the acrobatics rules as intending to make AoO and all related feats essentially obsolete.
maybe it is just overkill to add both dex and strength to CMD at the same time, at least without additional feat ?
I feel that the opportunity to make the attack should not be influenced by STR, but instead by Dex.Also, since it has both the Lightning Reflexes and Dodge feats, plus a dex of 20, I don't think "lumbering" is a very apt descriptor.
On a not-quite-related note, I still don't get why Dex is not a part of CMB, though
Oops!
You're right about the lumbering descriptor, I originally thought the greater water elemental had a DEX of only 10 - I must have misread.I guess we'll have to agree to disagree - For the same reason STR doesn't modify the bluff/feint DC (as pointed out by Singularity) I don't think it should modify the DC of Acrobatics.
You are correct in questioning DEX mods and CMB.
This is a big difference between D&D 3.5 and pathfinder. Whereas the Rogue in this case would have had no problem in 3.5, it is a near impossibility with these rules.
Just a quick FYI – I don’t play the rogue but I do have to heal him.
I'll take Dragon's advice and speak to the DM.
I don't see a problem at all. He could move normally like everyone does and not take that opportunity. If he is against a guy with a CMD 40 he shouldn't try to do that kinda stuff. Or try and suffer the consequences for failing.
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I agree with Xum.
Furthermore the issue that you bring up, the issue of adding strength to the CMD, has as much to do with the reason that the CMD was created = a fast and efficient way to resolve the check and not *have* to sit there and calculate bonuses. I mean you could extrapolate it out but at that point don't use the CMD/CMB system...
I also think that LazarX covered a further explanation early on in the thread.
Str is included to represent the power of main force as part of the quotient of the counter to your tumble.
Str isn't just that the Water elemental lifts big barbells, it strikes with force and mass to do its dirty work. You are advocating that the *power* of a 20 foot tall wave, should not impact how hard it is for a 5 ft tall guy to move out of the way of the wave. Strength is IMHO applicable because strength represents the force that the rogue has to fight against to accomplish his goal. Strength increases the velocity and force of the water elemental's swing.
A bullet flies straight, its dex sucks, but the strength is high. It is "fast" but not because of it dexterity but because of its force.
I do not tell my players the dc of their check flatout, do dm's actually do that ?
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I do not tell my players the dc of their check flatout, do dm's actually do that ?
Well the book tells the player the target and they looked out of game...I think in some groups it would be frowned upon to change the DC just to keep the player in the dark...or forbid them from looking in a Bestiary for that matter.
that can be solved.. water elementals with BARBARIAN LEVELS !
That oughta teach them.. looking into MY books .. at MY creatures.
hmmm.. what magic items could a water elemental use ?
Either way.. the DC for tumbling seems a bit too high in some cases, the sample was a rogue with full ranks, high dex and magically enhanced tumble it seems (dex 18 and + 5 competence bonus it seems).
The check was still too high to actually have a decent chance to make it, for a CR 9 creature against a lvl 9 rogue it seems a bit off.
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that can be solved.. water elementals with BARBARIAN LEVELS !
That oughta teach them.. looking into MY books .. at MY creatures.
hmmm.. what magic items could a water elemental use ?
Either way.. the DC for tumbling seems a bit too high in some cases, the sample was a rogue with full ranks, high dex and magically enhanced tumble it seems (dex 18 and + 5 competence bonus it seems).
The check was still too high to actually have a decent chance to make it, for a CR 9 creature against a lvl 9 rogue it seems a bit off.
Right but CR is for a group of 4 people right? I am sure that there are plenty of CR 9 creatures a Rogue would beat hands down and others that they would never live against...such is the way yeah?
As someone who has had to GM for a group that likes their rogues, nothing made me more mad then having characters under level 9 doing exactly what seems to be the "problem" here. Level 9 is higher than many, no doubt, but just willy nilly making AoO meaningless at that level for a class was irritating. Now in Pathfinder my Rogues actually have to accept that they can't always get away, on top off, or behind whatever they want, whenever they want. I personally think that makes it more meaningful when you actually can do that at higher levels...but maybe that is just my style?
I agree, to a point, but a check of 40 seems high, now I can imagine a water elemental to be especially hard to pass by really.
well checking further.. it seems 30 or so is the average CMD for a combative CR 9 type, considering a skill focus at lvl 10 adds + 6 it might not be so bad, the water elemental is just particulary effective at it.
The CMD was indeed created to have only one number to look at to resolve checks, and the rule is pretty clear, but that doesn't mean it can't be improved.
The checks themselves should have been reviewed along with the DCs, for one. It doesn't make much sense that the same ability to move around and against an opponent is on one side a skill and on the other a defensive combat maneuver. Skills should be opposed to skills and combat maneuvers to combat maneuvers...
The reason why that couldn't be is only that fighting types (and fighters especially) lack the skill points, and would have been disadvantaged by the first option, and roguish types would have been disadvantaged by the second. But now that creates aberrations : a fighter in full plate can stop a rogue running around more easily than a monk (taking into account MAD limitations - just as easily if not), for example. Or the strength bonus having an effect on the tumbling DC. The power of the strike coming on is already taken into account in the attack of opportunity roll, tumbling is supposed to allow to move without provoking that attack.
Of course, it's all a matter of personal preference. There's stuff you want to be really extraordinary, and stuff you want to be extraordinary as in "it's fantasy". But if we're going that road, I think most personal preferences would be that running around a dragon should be less meaningful than to inflict him massive damage with a dagger after escaping his blindsense.
Plus, are you sure that it gets better at higher levels ?
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Plus, are you sure that it gets better at higher levels ?
19th to 20th level Monster CMD looks to be in the low 50s...which for ten level highers than the Water Elemental seems a pretty big win in the "rogue" column statistically.
The CMD was indeed created to have only one number to look at to resolve checks, and the rule is pretty clear, but that doesn't mean it can't be improved.
Oh no, I agree. Its just that making things more complex doesn't necessarily mean improved, especially in a system based on abstractions and generalizations. I was just advocating that sometimes simplicity overrules purest accuracy.
The checks themselves should have been reviewed along with the DCs, for one. It doesn't make much sense that the same ability to move around and against an opponent is on one side a skill and on the other a defensive combat maneuver. Skills should be opposed to skills and combat maneuvers to combat maneuvers...
I see what you are saying, at the same time the skill in question is being used in the purest sense of the words "combat" and "maneuver", no? It seems relevant to me to cross check the numbers, especially in the name of simplicity, which I am a fan of, I will admit.
The reason why that couldn't be is only that fighting types (and fighters especially) lack the skill points, and would have been disadvantaged by the first option, and roguish types would have been disadvantaged by the second. But now that creates aberrations : a fighter in full plate can stop a rogue running around more easily than a monk (taking into account MAD limitations - just as easily if not), for example.
I am not sure what MAD is but I will say that, personally, the fighter as the paramount class for combat and tactics (as I believe them to be) should often have an opportunity to keep some leggy kid/guy/girl/elf/hobbit off their ass. Its what they are trained to do, unless they are distracted or seriously outmaneuvered...and not by some cartwheel kick to the left. Purely IMHO. It should be hard to get around someone who wants to beat your ass and is trained to do it.
I think the monk thing is interesting, but they are second best at a lot of things, I am not sure why this should be an issue, though I understand that this is something monks might be expected to "do". That said 3.0, 3.5, and Pathfinder have always made monks slightly less than ideal at their stated purpose at the cost of having many tricks so I see their diversity of talents being the counterbalance to why a guy, in full plate, trained to not be flanked might be better than a guy trained to pick rocks out of hands and climb tress really fast. ; p
And to be fair a guy who wears full plate is probably not that dexterous and so his CMD is not as good...
Or the strength bonus having an effect on the tumbling DC. The power of the strike coming on is already taken into account in the attack of opportunity roll, tumbling is supposed to allow to move without provoking that attack.
How fast you notice a guy moving might be Dexterity based but how hard the axe is to dodge is a function of its "power" as its "power" is its speed and force. Acrobatics is being used in an abstraction where everyone gets at least A swing in a round...so it makes sense that since that abstraction is present and implicit, the next thing to compare against is the force of the attack that might be made. A fighter might not be super nimble but being incredibly well trained to use power effectively to close the gap makes sense. If I am really strong I swing an axe faster than if I am really limber. The Acrobatics against AoO is as much about not being "hit" as it is about not provoking the attack - the abstraction being that no attack was granted because they couldn't hit you...they very well may have tried right?
Strength is used to represent both speed and power IMHO, Speed and accuracy as a function of the "to hit" and power as a function of "damage".
I was just advocating that sometimes simplicity overrules purest accuracy.
Well, yes. The question is, is that particular rule included in those sometimes ? I think not, for in making tumbling a little simpler to use it makes it notably less interesting to use.
It seems relevant to me to cross check the numbers, especially in the name of simplicity, which I am a fan of, I will admit.
It seems to me that having one system for all physical actions against an opponent, including feint, tumble, and the current combat maneuver (and maybe feats like fly-by attack or unseat), but with varying bonuses according to the action, would be simpler, and more elegant. But that would go to houserules/suggestions...
I am not sure what MAD is
MAD is for multi ability dependent. The monk need a good strength, a good constitution, a good dexterity and a good wisdom. That limits his bonuses compared to a fighter.
The fighter is not the paramount class for combat in any way. He's specialized in a particular type of fighting (the type he chooses, based on his equipment of choice usually), defined more or less by whatever is left after the other combat class specialization. The same way he's not supposed to go berserk in the middle of his fights or to sneak around to place a killing blow, he's not supposed to have the movement training of a monk. And we're not talking about a leggy kid that sneaks on some Witch-King, we're talking about a dedicated rogue with the same amount of experience behind him than the dedicated fighter. It should be hard getting in line with someone who wants to get out of line and is trained for it.And a guy who wears full plate put in strength what he doesn't put in dexterity. And in maneuvers that becomes agility...
How fast you notice a guy moving might be Dexterity based but how hard the axe is to dodge is a function of its "power" as its "power" is its speed and force.
But tumbling is not dodging. To use the power of your arm and axe, you have to aim first, because the more power you put in your swing, the harder it is to correct the trajectory. Speed and power is one thing (it's strength), accuracy is another (and I'd say it's dexterity).
If the abstraction is that they tried an attack but failed, the AoO when acrobatics fail should be an automatic hit. It's the contrary : if they tried an attack before succeeding in being ahead of the tumbler's move, it is an automatic failure.
I agree with Xum.
Furthermore the issue that you bring up, the issue of adding strength to the CMD, has as much to do with the reason that the CMD was created = a fast and efficient way to resolve the check and not *have* to sit there and calculate bonuses. I mean you could extrapolate it out but at that point don't use the CMD/CMB system...
That's another good point. The rogue may want to tweak the system in this case, but when his dex and BAB mods are suddenly taken out of his CMD when someone with a grapple on him starts doing damage because, "it's just question of strength!," he won't be too pleased.
It's imperfect, but not a huge problem imho.
But tumbling is not dodging. To use the power of your arm and axe, you have to aim first, because the more power you put in your swing, the harder it is to correct the trajectory. Speed and power is one thing (it's strength), accuracy is another (and I'd say it's dexterity).
If the abstraction is that they tried an attack but failed, the AoO when acrobatics fail should be an automatic hit. It's the contrary : if they tried an attack before succeeding in being ahead of the tumbler's move, it is an automatic failure.
I guess the illustration would be like this: on one side you have a 4'2" 90 pound guy who's 85 years old with a 40 pound sledgehammer, and on the other side you have a 6'6" 280# guy who's 24 years old with the same skill as the older guy with an identical 40 pound sledge; the only difference is their strenght, but wouldn't you think it would be easier to get by one before they can get a swing off on you than the other?
And again, this situation IN NO WAY limits the utility of tumbling; against any but a handful of CR 9 creatures the rogue is going to be virtually immune to AoO; THAT is a VERY POWERFUL ability. If it were designed to make the acrobat universally immune to AoO, it would be extremely unbalancing. There are only two creatures with CMDs of 40+ at CR 9. Two. Do you really find it unbalancing that there are two creatures of an appropriate level that are a threat to AoO the rogue?
A rogue can deal with grapples with the escape artist skill on his turn, better than with his CMD - he will probably lose in any case when a grapple is initiated. But anyway, the point is to have a simple, elegant rule that sticks to the action, not to please the rogue players. If they've got an undue advantage in another situation due to the same rule, that just proves once more that the rule is bad.
I don't see the point of your example, you add too much different variables. It is easier to pass by an old guy with less reach... but the rules for old age decrease both strength and dexterity, as they should, and neglige the difference of reach within one size category. Let's say there's a strong guy and a weak guy, same dexterity and reach. What reason is there for the strong guy with his bastard sword to be able to get a chance to hit (an AoO is not a hit) more often that the weak one with his rapier ? None.
And the intention of the devs was to limit the usefulness of tumble. They made no secret of it, they tought the fixed DCs of 3.5 made it too easy, so they limited the chances of success. Though I think the fixed DCs were bad design, and it did need to scale with the opponent, I don't think the ability itself needed a nerf. Rogues should have difficulties escaping a monk or another rogue of their level, but escaping a fighter is all this ability is about. Concerning monsters, obviously that depends on the monsters. But the norm should have been a success rate of, say, 3/4 for normal monsters, and 1/4 for particularily agile monster, who're supposed to beat most of the time a rogue of equivalent level at what he does best. Now it's a gamble already against most monsters, and an automatic failure against the harder ones. He's in no way immune to AoO against common monsters of the relevant CR, there's no need for an automatic failure to constitute a threat.
And of course the ability has still a use. Even if the primary attack roll was successful just half the times it is now against common monsters, that would still be the only way to hurt them, and thus be VERY POWERFUL. That doesn't make it the ideal way to play it.