Mike Tyson Riddick Bowe Naseem Hamed James Toney Tyrell Biggs James Tillis Frank Bruno Marvis Frazier
There's a great example. This guy almost had Camacho when he was a legit fighter. He was a pure dark horse when his talent was raw. Then once he got noticed he was already "past it". When he was physically his best you'd assume he dominated in his prime, but not with Rosario.
Pender in particular is a great shout. For someone who really didn't like the sport, and who had a reputation as a negative fighter, he certainly produced some nice results. Vernon Forrest was always kind of a tough fighter to read in terms of performance and career trajectory, too.
Exactly how good could Jerry Quarry have been with the training habits of a Marciano and the mentality necessary to always fight the right fight against the right opponent? He was psychologically destroyed in the Ali rematch. The luck of the Irish was not with him, yet he raised hell anyway, and defeated first rate opponents in every manner possible, getting off the deck to take out Alexander, coming back from an eight round shutout to knock out Zanon in nine, dominating a peaking Spencer from beginning to end, blowing out Bodell and Shavers in one, handing an undefeated Lyle a boxing lesson, and coming from way back to beat up a peaking Mac Foster. (Mac was awesome in that match, adding much lustre to Jerry's win.) Quarry was never going have a chance at defeating Ali, unless he somehow avoided getting cut in Atlanta. (Even then, Muhammad's heart would have pushed him through any fatigue.)