He was winning the punch exchanges with Gannon. He has zero cardio and that is why he lost.
Against Fedor or Mirko he would be beaten standing or on the ground handily.
In MMA, the most Kimbo could ever be is a less talented Tank Abbott, but facing tougher comepitition then Tank did in his day. In otherwords he would suck

In boxing, he would never have the cardio or speed to beat anyone. He's top rate when it comes to short fist fights with smaller versions of himself. I'm sure he could beat the hell out of 99% of people walking down the street.