Comparisons to other eras no matter what sport are absurd, first of all the training, diet and professionalism simply wasn't there back in the 30's.
Athletes, be it Footballers, Basketball players, Baseball players, Hockey players, Cricketers, Cyclists and Boxers etc are all full time professionals these days and if they are not cheating then they put themselves through rigorous training regimes and are all on special diets to maximise performance and longevity in their chosen sport.
Holyfield is way off the mark here with his comments, Louis and Owens were greats of their time and had they of had the advantages he has had then they would have been greater!
Almost all of our past sporting heroes were part-timers and their achievements were exceptional given their circumstances. Does Holyfield think that both Phelps and Bolt's achievements in Beijing will not be surpassed given time? Holyfield has taken to many punches.