I might agree that training techniques have not changed much and therefore there isn't a great advancement - however, I will disagree that nutrition hasn't changed much and that supplements are not available that are legal and can be taken that make fighters better.
I will agree that a champion is a champion, if a real champion. Perhaps it's the alphabet soup that has me more questioning whether certain paper champions would have competed with the best... but if you compare the best of one era to the best of another area, I think that you more can go with the strengths and weaknesses of the fighter as compared to other factors... it's the middle of the pack that is hard for me to compare - the second tier guys as opposed to the greats.
The one exception to that would be heavyweight. These guys are bigger than the previous era's heavyweights. It would have been difficult for the former heavyweight champions to imagine the size and quickness of today's heavyweights - as well as to imagine their lack of technical skills and conditioning. Rocky IV somewhat characterized what that might look like, when you look at Drago's sheer size and power versus a smaller, quicker Apollo Creed. Not a thudder like Rocky (Tua/Tyson) who would bang no matter what... but a quick champ (Byrd) is pretty well lost against that size of a champ despite good technical ability.
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