People say this about everything. "If they nerf it something else will take their place" isn't a legitimate rebuttal. Someone will take their place, but they won't be as goddamn ridiculous as the previous character was. See Sagat in Street Fighter IV and Diddy Kong in Super Smash Bros. They were absurdly unfair, and while there have been plenty of top tiers (who have also subsequently been nerfed), nothing has come close to how ridiculous they were, and the games were much, much better for it. No matter how they end up fitting into the metagame, whoever replaces McCree's role will be nowhere near as ridiculous as an AoE stun with an 8 second cooldown and an attack that does around 400? damage in less than a second.