Good question. I think Frazier might have some issues with SOME of the later heavyweights. That doesn’t say he struggles with all or even most. But it seemed like the bigger his opponents were the harder they were for him to beat.
Foreman, at the size he was in the 70's, wouldn't be able to rely on his size and strength. Ali wouldn't be able to rely on his personality and clowning for the refs. Frazier and Quarry would have to be cruisers. Norton would be shellshocked. None of them could compete as they were and only Foreman could truly compete at the top level.
Don’t you think Usyk showed that older smaller fighters would still be competitive ? Would you not favour prime Tyson against most of the recent crop ?
Smaller fighters such as Joe Frazier would have struggled with some but I would still back him to beat most of them.
Usyk is the exact size as Foreman was in the 1970's but rather than being a size bully he has been a shifty, elusive technician, all of which goes to prove my point.