CubicsRube
Hero
Well, a nitpick here is that Sharpshooter negates cover so that doesn't change anything.
More importantly, your post proves the point.
If the game needs to be changed/difficulty raised/targeting a specific PC all because they have taken 1 of 2 feats then those feats are too good.
Taking SS or GWM (SS is the worst offender here) increases a PC's damage by about 50%. At level 5 the Sharpshooter Fighter or Ranger will be doing 50% more damage than the Rogue. The +10 is as much damage as the Rogue's Sneak Attack. So the thing they're supposed to be good at, getting precise shots, is being done better by other characters.
It doesn't matter if the DM makes it an arms race with the players, that one PC is much stronger than the others in combat. It will depend on the group whether they are okay with that. It might also incentivize them to start taking those feats for the power over other character concepts which would be unfortunate.
I personally don't mind playing in groups of characters with different levels and/or large magic item disparity. Even I don't really like the idea of having that be a character choice though.
Youre right about the cover bonus, I'd overlooked that.
But it doesn't negate my point.
I never suggested changing the game because kf those feats. They are however often brought up so I thought I'd bring up examples.
Fighting near lava or a swamp? Obscured vision. Disadvanrsge to everyone on attacks.
Pitch black cave? Diaadvantage to everyone unless within range of a torch for which i would grant disadvanrage on the attack as per obscurement (note darkvision only treats pitch black as dim light, not bright)
If the foes are intelligent, they will often focus fire on the biggest threat, which may be a caster, a sharpshooter, gwm etc.
Those are just general tactics regardless on whether feats exist.
I have played 5e on an almost weekly basis and found now problem with feats in our games. Many times GWM isnt used. I had a ranger with sharpshooter and he could sure shoot well, but that was his shtick, and he still didn't use it when he needed to make sure he hit. And by that time the wizard is casting evards black tentacles and wall of fire and tying up half the encounter.
Spells (such as wall of force or banish) are a much bigger encounter killer than feats