No way - disagree. Footballers of course are much fitter and conditioned than even 20 years ago, but there have been changes in boots, balls, pitches etc too so I'd never make direct comparisons there. In professional rugby union, almost a different sport I'd agree, as players are complete freaks nowadays. Tennis again I'd agree with you with developments rackets, footwear etc.
But boxing is two people face to face. Ali, Frazier etc would train and condition for months. Just look at the brutal battles they had, 15 rounds in searing temperatures. Neither Usyk nor Fury has the skill of Ali, or indeed power in the case of say Frazier, Foreman or Tyson, hence my comment. So comparisons are easier with boxing in my opinion than many other sports.