You think Tyson was past his prime at 23 years old? ...'cause that's how old he was when he lost to (lowly) Buster Douglas. And he never beat a good fighter after that (with the possible exception of Razor Ruddock). In fact, Tyson never beat a top-notch fighter in his whole career. (Holmes was an old man when they fought, and he lost to Holyfield in both their fights).
Tyson, is most overrated heavyweight in history, without question.
Even Ali, who I would put at the top of fighters I've seen, had "down" fights in his prime. Ali was much smarter and better disciplined than Tyson (a huge understatement), so he didn't have the same disastrous results. Still, it's hard to discount Tyson's power and instinct.