I agree with @GreenFlashlight when it comes to 'encounters have to scale to meet the abilities of Billy Badass'. I'm on a DnD game right now. I play a (fairly) powerful character with a fairly decent build, but I've tried to make him the sort of character that can solve a variety of problems while still being combat-capable.
Save that the other players have hyper-focused on sword-swinging because sword-swinging is pretty much all they care about. Not solving mysteries. Not finding alternatives. Just hit the thing until xp falls out. It's basically Final Fantasy.
Which means that my versatile guy, that has a ton of utility in a lot of ways, is pretty much useless in combat. He can dish out a LOT of damage in a turn, granted, but his saves are absolute shit compared to the DCs these beefed up monsters are throwing out, and it's hard to hit something so scaled up in AC as to keep the Level 20 Paladin of Smashing from one-shooting him.
But more than that --
It's been my experience that the people that hyper-focus on the numbers aren't in it to play the same kind of game that I am. They're in it to win, and get frustrated when they don't win. They will find every excuse in the book why that roll that they failed shouldn't have failed because, see, it's right here on the sheet, he can't ever be intimidated by anything, ever. All that muscle mass makes him immune.
And this isn't limited to just fighters and martial types. The people that over-optimize for a certain thing always have trouble when presented with something else, and will seek to turn it back to what they've specialized for. Diplomatic talks? Good luck, because that fighter is gonna punch that guy, and then just do some Big Stick Diplomacy. Glad you greed to our terms, I hope there wasn't too much concussion.
A certain amount of strategy is good. But if all you're focused on is getting your sword-swinging number as high as it will possibly go, then we're gonna have problems.