The problem Tyson had- all D'Amato and Rooney fighters had- is that their style is reflex based. Jose Torres got around this by retiring early. Floyd Patterson quit using the 'peek-a-boo' after the first Johannsson fight; indeed, he'd already started to phase it out. With that style, you constantly have to react to straight punches, always be slipping jabs and right hands. And you are vulnerable to uppercuts. A good fighter- or Buster Douglas on a good night- will land that jab, then he'll start to feint it, to make you react, and look to land something meaningful off your reaction to the feint.
What happened to Tyson was, he slowed down a little bit, probably due to not training as hard initially. And then he had that bad cut in sparring and started sparring in full head gear, which got him in the habit of standing up straight. (to see under the head gear, a pretty common problem.) Then he was just a short, short-armed fighter with some quickness and a big punch. Some guys he could makes a move on, get in and do damage, others, not so much.