I'm thinking about it like this. If McCree catches Trace/Genji/Reaper in a hallway they deserve to die, straight up. With a highly skilled player those three can be an absolute nuisance (especially Tracer) that have fantastic escape options. If they get close enough to McCree where he's aware of their presence, they fucked up. If they round a corner and McCree is there, they fucked up. If they run up on McCree's team capturing a point and get in the middle of the throwdown, they fucked up. The problem is McCree can kill characters without great movement options (the tanks) with the double fan combo. If you wanna argue his primary fire is too good that's one thing but the flash + fan combo wasn't an accident.
I feel that they deserve to be at a disadvantage, not that they deserve to automatically die regardless of of a players skill level because they stepped into his range. Everything in the games design should be at least partially skill facilitated, and McCree's go-to kill method isn't that at all.
Even if McCree didn't have a stun at all he would still be at an advantage in those circumstances. Stun has absurd utility, putting aside the instant-kill, it can also pull just about anyone out of their ult. Genji, Reaper, Roadhog etc. he pulls them right out of it. Not only is McCree absurdly good in his own right, his stun makes him a counterpick to all other on the ground offensive options. Logically, Pharah would be his counterpick since he is stuck on the ground and has high close range efficacy, but she's not, in 4 shots he can down her at mid-long range, even faster with a bit of luck and fan the hammer.
Only tracer seems like a counterpick to McCree, but they seem pretty even. The problem is that you have this idea that he is 'bad at range' therefore he is balanced out by this weakness, but he isn't bad at range at all and at the same time he is so good at close range that he completely nullifies the efficacy of other offensive heroes.
I think fan the hammer is fun and the fan the hammer roll combo actually requires some skill with the opportunity for opponents to outplay you, it's just the stun and the ranged damage that fan the hammer can do that are an issue. Fan the hammer should have more damage drop off, and I think his flashbang should be a blind, not a stun, providing players some opportunity to counter with their kit.