Did Tunney have a prime. Seemed to retire as he was peaking. Bowe and Douglas are good calls. Johansson is too. Three guys who were undisciplined and it showed as soon as they won title.
Foreman would be my pick, even if it was quite subtle (or not, depends how you look at it). I think his style tweaked in a way that did not suit him after Zaire
it could be argued Bowes stretched the entire 3 Holy fights even not winning them all, Busters to me was even shorter,,,
Well, I was just looking from when he became Champ to when people consider him to be past prime. '62-'64
Come now. Sonny Liston decimated the division prior to being champ. People forget that he was made to wait years for his shot. Tyson also decimated said division over a few years. Frazier did too. Buster Douglas was a ranked contender for a couple years before Tyson. Just cause a guy held the title briefly doesn't mean that he didn't have a prime. Being a contender counts for something. Even Leon Spinks, erratic as he was, had to be considered a handful from about 1977-1981. Perhaps Ingemar Johannsson. This is an interesting but hard to answer question, due to the many possible definitions of 'prime'.