They already have a power-copier dude :V.

I read somewhere that the original idea was that he would remain power-less and just be a hero with his normal-people muscles and brains, which I find more interesting a concept then either power-stealing or ONE PUNCH ing. I doubt it would have gotten as big as it did if it went with that, and can see why the author made the choices he did, in the end "what iffs" are kinda pointless anyway :P