Is every top heavyweight boxer on steroids these days?

If you compare the physiques of guys like Muhammad Ali or Joe Frazier and guys like Anthony Joshua and Wladimir Klitschko, there's an insane disparity of muscularity between the two. Is it really just "genetics" and "better sports science/diet" or is it just simply substance abuse? I mean, boxing training hasn't changed much at all since the Ali-Frazier era, so I'm kind of perplexed at how a guy like Anthony Joshua can supposedly "naturally" achieve a physique that Ali and Frazier couldn't no matter how hard they worked.

boy boy

the facts are that we all are bigger than our ancestors ..and for a modern just take north and south korea...the people from the north are on average 5" shorter than their southern neighbors ...poor diet ..ali never weighed much more than 15 stone ...henry cooper 14 stone ...nowadays its 17 stone average ..and above ....drug abuse ? its boxing ...not WWE