Dear Paizo,
I am loving the new PF2. I am just a little bit concerned about the "weight" of the level bonus compared with ability or "training" bonus.
I understand what have you done. You have tried to simplify and merge skill and attack bonus, as long as it is just to calculate a modifier to get through a DC. I think that this makes lot of sense and reduces the complexity of the game without affecting customization/fun.
The problem is that while in combat it makes sense that the experience (level) becomes key for skilled people, for skills ... well training should be more important.
So far at lvl 6, for skills, a character can get a +6 from level,+3 characteristic, + 1 training, +2 item). A + 12, where the 50% of the bonus is due to level. The items can be purchased, therefore, the 75% of the bonus is due to the character level.
Then I understand that to counter that you have said that the skill level "untrained, trained, expert" it is not only about the bonus, but also about what you can done and skill feats. Good idea. The problem is that in my opinion, especially the first, makes the game too complex, as GM tunning one parameter, DC, it is easy, but tunning 2 parameters DC and training required might be a little bit challenging.
So I would propose that instead of getting a +1/level, you get a +1/even level and double the skill training modifiers.
In the previous case, for instance, now the PC will get (+3 level, +3 characteristic, + 2 training, + 2 item) a +10, where only the 30% of the bonus is due to the level.
Could this system be applied also to the combat? Well, this could be done, but it might be tricky. The problem with this is that you will get the same AC, and then decrease on the attack bonus might hurt your hitting chances quite a lot. Of course, we could decrease the bonus of the armors, and while this might work for heavy armor, this wont work for DEX based AC. Furthermore, when you have magic items, the armor bonus to AC becomes less important. We could change the system so heavy armors provides apart from AC, DR or critical hit protection. But from the mathematical point of view i see difficult to find a balanced way to do it.
So, my opinion, is that it will be better to have two proefficiency bonuses, 1 for saves and combat (i dint discuss this here, but yeah, it is similar), and other for skills.
Additionally, I think that neither on PF neither on PF2 is is highlighted enough the neccesity of circunstancial bonuses on cross-skill checks.
For instance, is you want to sneak around a guard, you roll stealth vs perception. However, it should be taken in account the circunstances, if its day, or night, or things like that.
Finally, regarding the accumulation of bonuses, I would suggest to simplify it basing it on the "source" than on the "type". For instance, a system where you can only add three type of bonus, the highest coming from the item (even if they are different bonus type), the highest coming from the circunstances, and the highest coming from you (spells, ancestry,..). Sometimes it becomes a little bit annoying to make the checklist of the bonusses you have. This will simplify the calculations.