I’m not convinced many after 1980 are clean. You also left a lot of the other “athletes” off the list. FYI human evolution has not occurred in the last 100 years. The human body can be trained into the same shape in 1920 as it could in 2020. You also call these people athletes and they”re winded after six rounds. That’s not really athletic. They just traded certain traits for others. Are Louis Charles Walcott Marciano Patterson not athletes?
I don't disagree, PEDs play a huge part in sports and boxing is not an exception. It seems obvious that a few heavyweights learned of the benefits of PEDs in big time boxing in the 60s. There had always been 6-3 and taller heavyweights, but their height advantage had been negated by their relative slowness and awkwardness. In the 1960s some of the 6-3 heavyweights started to "fill out", they became quick and strong, they weren't lanky, slow, and awkward anymore. They were suddenly "athletic." Then in the 70s there were more of them, the 6-3 heavyweights who in the 40s-50s had been lanky, relatively slow and uncoordinated became muscular, fast, and athletic...then from the 80s on, the big, fast, coordinated athletes were common place and eventually the 6-3 heavyweights were average height and there were good 6-5 ones, and now the 6-5 heavyweights are considered average height and are being replaced by taller ones. People didn't suddenly evolve after 1960, it's just that boxers and trainers learned about PEDs and the PEDs allowed bigger people to become better athletes. PEDs make athletes bigger, stronger, faster, and PEDs allowed them to recover quicker when they train. Boxing, like all sports changed, the athletes are bigger and stronger. It didn't happen by evolution but it happened. There is also the argument that better athletes got involved with boxing after the Ali - Frazier fight in 1971 where the fighters split a then unheard of $5M. No doubt that is true, but IMO, PEDs made a bigger difference.
Saying the difference was just PED's is far too simplistic. It had much more to do with greater recruitment of athletes, the recognition of the role of modern strength training, and an expanded net to cast for talent.. Africa, Eastern Bloc...