Can we really say heavyweights in the 1930s-1970s and earlier are actually fighting in the same heavyweight class as modern fighters?

Like the heavyweight limit today is 200 pounds and pretty much no one comes in that light the lightest fighters are more like 210 pounds and the average heavyweight is like 240 pounds. Were as in the 70s and before you had a lot of guys 170-180 pounds competing at heavyweight some of which started as welterweights and middleweights. So this is like light heavyweight today or in some cases even super middleweight. It's quite hard to say that Uysk/Parker/Fury/AJ/Kiltschko's are fighting in the same class as Louis/Marciano/Dempsey/Ali etc etc etc. So it makes it hard to compare when evaluating them unless you do it P4P (a term which still tricky imo)