Sharpshooter will be both buffed and nerfed, right? It (along will all ranged attacks) will be easier to hit with. However, BG3 is not going to have both cover and height-bonuses, so the "your ranged weapons ignore half and 3/4 cover" aspect of Sharpshooter will be useless. I think this probably works out to a relatively small net buff.
I agree that cover and height bonus would affect the fights differently. But I don't think either case is better/worse than the other.
Can you please explain why combats would be rudiculous ?
I understand the concept of bounded accuracy but I don't get why a single +1/+2 bonus would break combats. As a vidéo game player, I see it as another reasonable tool to control our %to hit.
Height bonuses are Larian's homebrew. Sharpshooter essentially gives bonuses by removing penalties to cover. Without cover mechanics, you have to provide Sharpshooter something else since in BG3, that portion of the feat is meaningless. So what is Larian to do? They'd have to give SS more bonuses to compensate for lack of cover. Like you said, AC and to hit mods are the same mathematically.
It would be ridiculous if you provide SS with more and more bonuses when the whole point of balancing that particular feat is reducing them due to the -5/+10 mechanic. It's the same problem we are having with GWM. All a fighter has to do is jump, go behind a mob. Now he has advantage which pretty much negates the -5 penalty and essentially gets free +10 damage per hit with a greatsword or polearm. It's a joke. Throw in dipping and we get absurd levels of damage. Let's add level 5 extra attacks and action surge. See where this is going?
Because of how little accuracy and AC changes in 5e, every little bonus makes a significant difference on rolls. That +2 to hit may not seem big but it potentially makes huge differences on how many times you hit. Interestingly enough, Larian knows this and that's why they are giving out advantage like candy. They have the notion the characters weren't hitting enough and that's boring gameplay (it's a fair observation). But if characters hit too much, creatures die too fast hence we are getting mobs with higher than normal HP. Larian is trying to rebalance what has been balanced long ago and now are dealing with all sorts of balancing issues, mainly from all their homebrew.