I say if the gap is larger than 2 or 3 decades eras shouldn't be compared
Many fighters fight through multiple eras, so this idea of the new era athletes being "better" is not always true. Look at how many eras Duran fought through.
The heavyweight era that is currently around is complete garbage and should just be forgotten. The weakest duo of champions ever witnessed and an incomprehensible decline in skill and talent. When your 6'6" frame is the the only thing saving your egg jaw from being cracked you know its a bad era.
Bowe, Holyfield, Lewis, Tyson and even old Foreman, Mercer, Douglas, and McCall would thrash this weak era. Any one of those guys would become undisputed today.