I may be a broken record for focusing in on this, but it's a problem I have absolutely seen in my games - or at least a problem that makes players I have played with focus down certain paths and not take other options.
Quick preamble about the issue:
Without feats, the various fighting styles have been designed to keep things really balanced between different attack styles. The issue comes with how to boost damage in the game where there are only two attack styles that are able to do so: Sharpshooter and Greatweapon Master.
I have been workshopping a catch-all damage boosting feat with a different flavor that would appeal to a large number of characters. The problem is that it immediately gets criticized as being too good of a feat since it covers about 60% of the weapons in the PHB versus Sharpshooter or Greatweapon Master covering a much smaller pool. I have tried to talk to others about how many feats to break it up into, but it's always a question that gets more difficult to solve.
I would say you can just prune the damage clauses off, but I like the option of extra damage. It makes combat move faster - especially with lower AC targets with a lot of health and encourages trying to get advantage on an attack. It is indeed easier to prune than to make a bunch of new options though.
OK, so my current thought is to just add this blurb to the "Attack Rolls" section of the "Actions in Combat" section of Chapter 9 - Combat in the PHB (on page 194):
POWERFUL ATTACK
Sometimes a player has found themselves in an advantageous position, or against a foe who more stubbornly clings to their life. Before you make an attack roll with an attack you are proficient in, you can choose to take a -5 penalty to the attack roll. If the attack hits, you add a +10 bonus to the attack's damage. Yes, this includes spell attack rolls. The goal for the moment is to let combat move quickly - for both players and NPCs.
However, I dislike cutting a large portion of what makes Greatweapon Master and Sharpshooter flavorful feats; just like I hate that the Grappler misprint limits its use. So I would make the following modifications:
GREATWEAPON MASTER
You've learned to put the weight of a weapon to your advantage, letting its momentum empower your strikes. You gain the following benefits:
When you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action.
Once per turn, you can force a creature you hit with a melee attack with a heavy weapon that you are proficient with to make a Constitution saving throw. On a failed save, the creature gains the stunned condition until the end of their next turn. The DC for this effect is 8 + your proficiency bonus + your Strength modifier.
SHARPSHOOTER
You have mastered ranged weapons and can make shots that others find impossible. You gain the following benefits:
Attacking at long range doesn't impose disadvantage on your ranged weapon attack rolls.
Your ranged weapon attacks ignore half cover and three-quarters cover
When you make a ranged weapon attack, you can use your bonus action to aim your attacks with pinpoint accuracy. Until the beginning of your next turn you can try to shove a creature with your ranged attacks. If you use the DMG additional actions in combat this would allow actions like Disarm or Mark as well; the intent to to allow for reasonable trick shots that otherwise cannot be attempted.
Yeah, I realized I was thinking of "Dazed" from Pathfinder which is incapacitated in 5e, and I didn't think of the situation where multiple player take this. I don't even think prone is a terrific idea because it gives advantage to attack rolls after it.
For Great Weapon Master, maybe change it to a Strength saving throw to avoid being moved 5 feet? Or a Wisdom saving throw to avoid being frightened for 1 round (Charisma-based DC).
This would encourage tactical thinking by the players and presenting interesting terrain by the DM: pits, difficult terrain, campfires, caltrops, hunting traps, cracks in the ice, pools, traps triggers in general, etc.
Yeah, that's the exact type of thing I was going for - status effects/forced movement/etc because that is a good use of a feat that isn't direct damage. The problem is that "overwhelming power" sort of lends itself to a narrow range of effects.
I have been thinking on and off and came up with adding two lines to replace the -5 penalty to attack for +10 bonus to damage.
When you make a melee attack roll against an object with a heavy weapon you deal maximum damage.
When making the Shove action against a target with a heavy weapon, you can choose to move the target an additional 5 feet.
I think it would be fun (but maybe not balanced) to have you move your target a number of feet equal to the damage done (rounded down to the nearest 5 feet, if using the "optional" grid rules).
So 2d6+3 would average 10 feet moved, occasionally 5 feet and sometimes even 15 feet, and maybe even 30 feet on a critical hit with maximum damage.
GREATWEAPON MASTER
You've learned to put the weight of a weapon to your advantage, letting its momentum empower your strikes. You gain the following benefits:
When you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action.
When you hit an object with a melee attack, you deal maximum damage instead of rolling dice.
When making the Shove action against a creature with a heavy weapon, you can choose to move the target an additional 5 feet (10 feet total) as a bonus action. This distance is increased by 5 feet when you reach 5th level (15 feet), 11th level (20 feet), and 17th level (25 feet). If an obstacle prevents the creature from completing its movement, it falls prone next to the obstacle.
GREATWEAPON MASTER
You've learned to put the weight of a weapon to your advantage, letting its momentum empower your strikes. You gain the following benefits:
•When you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action.
•When you hit an object with a melee attack, you deal maximum damage instead of rolling dice.
•When making the Shove action against a creature with a heavy weapon, you can use a bonus action to move the creature a number of feet equal to 5 times your proficiency bonus. If an obstacle prevents the creature from completing its movement, it falls prone next to the obstacle.
10 feet at 1st, 15 at 5th, 20 at 9th, 25 at 13th, and 30 at 17th. It's not that much more than what you propose, but it's a little less wordier, and slightly less "rules-meta" (?) than using specific character levels and adventuring tiers. Granted, that's how cantrips work, and possibly how Fighter Extra Attacks SHOULD work...
I've been thinking about this a little bit (since my players have a similar tendency to rule anything out which can't benefit from Sharpshooter or Greater Weapon Master). I would come at it from a different direction than you.
Partly, that's because my preference for houseruling is generally to be additive, rather than adjusting rules which already exist.
I also think that people overvalue DPR as a measure of valuing styles. It has the advantage of being an objective, easily calculated, linear scale. However, there is a significant difference between fewer large attacks and lots of little attacks - even if the GWF out DPRs the two-weapon fighter, they waste more damage (by taking the opponent to massive negatives unnecessarily). A two-weapon fighter can distribute their attacks amongst more opponents as they start to fall. So even if they're a little behind in DPR calculation, they may not be in terms of 'number of enemies dropped in a battle' which is actually what matters.
As such, I think a TWF feat which boosted its own niche (like "When you make a bonus attack with your off-hand weapon, you can make two separate attacks, each at -2" or something) would be my preferred direction.
I think applying a penalty to an extra attack is probably a bad idea. One of the great features of 5th Edition is how streamlined and elegant it is. Adding and subtracting lots of little numbers is more in the style of Pathfinder, not 5th Edition.
For the most part:
Granted, in the 5th Edition conversion of RotRL I played in, we had a ranger with Sharpshooting (-5 to attack, +10 damage), Archery Fighting Style (+2 to attack rolls on ranged attacks), hunter's mark (+1d6 to damage), bracers of archery (+2 to ranged damage rolls), a magical bow (at least +1 to attack and damage), often magical arrows, and usually was under the effects of bless spell (+1d4 to attack rolls and saving throws) from my cleric. But he has a lot of rules mastery, and actually prefers Pathfinder, if I understand correctly. But that's still 1d20 +1d4 +2 -5 +10 (+5 Dex, +5 proficiency) +2 on attack rolls for 1d8 +1d6 +2 +2 +5 +10 damage. 1d20+1d4+9 for 1d8+1d6+19 damage??? Why have I never done all this math before? No wonder he was our major damage dealer!!!
Maybe allow 2 attacks as a bonus action, but with 1 (or both) at disadvantage? Like the goblin boss's Extra Attack from Multiattack.
Or just make the requirements stringent enough you don't need to apply penalties, like:
Greater Dual Wielder Prerequisites: Dual Wielder, Proficiency in Dexterity saving throws, Extra Attack class feature or Proficiency Bonus +4
You have truly mastered the art of fighting with two weapons, gaining the following benefits:
When you use your bonus action to make an off-hand attack, you can make 2 attacks.
You can use your reaction up to twice per round, but your second reaction can only be used to make an opportunity attack.
When you are wielding two weapons, you roll initiative with advantage.
I figured disadvantage was too tough but unpenalised was too lenient. Perhaps disadvantage on the extra granted attack would be 'about right'.
I must admit I didn't put too much thought into the specifics - I just wanted to make the point that I'd go for providing extra feats rather than modifying existing ones.
I agree. I think new feats are a better design strategy than re-writing feats.
Is 2 reactions a round too much? Would "You make opportunity attacks with advantage" be better? Or should it specify that the second opportunity attack must be made with a different weapon than the first opportunity attack?
Personally, I don't think two opportunity attacks is too much (two unrestricted reactions would be, imo). I don't mind giving players things like that: most battles it won't make a difference, but every now and again it's awesome. That's the ideal for a player-option, in my view. You don't want it coming off all the time or everyone will take it, at the same time you want the player to feel like they made a good choice when it does come into play.
I chose to follow the cantrip wording because feats are most like spells in terms of wording so I felt it was most clear (though I like your (SmiloDan's) wording better).
I don't like the bonus action attacks for great weapons, because I was trying to streamline "fighting styles" where polearm master, monks, and two weapon fighting gets more attacks. Giving that to great weapons twice seems counter productive and stepped on toes a lot.
I've also been tinkering with feats I have found to be underwhelming in practice (like Dual Wielder), or feats that had lines removed from errata (like Grappler or Tavern Brawler). What I'm spiraling toward is cutting my house rules to 5e down to 1 sheet of paper to accompany the DMG variant rules I use with that campaign.
So far, I have:
Spells with attack rolls can be used with sneak attack if the roll is made with advantage
Careful spell metamagic can also be used to cause no damage from the targeted creatures
Reactions cannot be used to react to a reaction
Some forced movement provokes a reaction (falling, shoves, generally anything that doesn't target an area of effect)
You don't fall unconscious at 0, but are seriously injured until healed
Spells that are cast as reactions can be cast using a bonus action - this is a cascade from my earlier reaction houserule
A firearms feat like crossbow expert
Dual Wielder gives a bonus +1d10 damage to offhand attacks when the main hand attack lands
Grappler lets you grapple larger creatures, but not pin them (only hold them in place)
Tavern brawler makes unarmed strikes light weapons
Right now, I'm making 5e a little more OSR feeling slowly and tweaking on the way. Eventually I want to cut HP totals logically, and give a feat for each of the weapon groups. We have light, finesse, heavy, ranged, and reach weapons along with non-monk unarmed strikes, shields, and the grapple action. I'd like to cover the shove action, monks (but not exclusive to monks), throwing weapons, versatile weapons, and something like fell handed focused on the weapons with no properties (mace, flail, morningstar, and war pick).
EDIT
I feel I should be clear that I'm not designing DMG material here - I just like being DM and I like 5e, so I'm dialing in where I want it to be.
Did they nerf enough that you could combine Grappler and Tavern Brawler into a single feat?
EDIT:
I was working on an Exotic Weapon Proficiency feat where you select a number of weapons equal to your proficiency bonus, and add a weapon quality to each of them. When your proficiency bonus increases, you may select an additional weapon to exoticize. For example, you could Versatile or Reach to the flail, or Finesse to the handaxe, etc.
Well Tavern Brawler as printed gave proficiency with unarmed strikes as a benefit of the feat - and obviously that is a rule cooked into the system. All I did was was enable TWF with an unarmed strike (like a kick after a sword slash) with unarmed strikes.
I like the idea of a weapon "formula" for custom weapons.
