Really they had different and impressive careers. I don't think there's much need or purpose to direct comparisons. Floyd probably has the better wins, and certainly more quality wins, while Rocky did it in the riskiest division, despite a much higher risk style, and did it, rather simply by fighting the best in a single division with a single title.
It's a fairly pointless criterion since Louis was way past it, Charles was past it and above his best weight, and Moore was pushing 40 and fighting in the wrong weightclass, though still good.
I believe that you can only fight the professional boxers of your era, not of the future or the past. Rocky Marciano, fought the best that were around in his time. Floyd Mayweather fought the best in his era. We imagine these dream fights theoretically, but one cannot criticize a pro boxer on his competition. We can only assume the outcome, which makes these threads interesting. Everyone to their own opinions. Both fighters 49-0 records were special.
If Rocky were around for as long as Floyd, he would've run into Patterson, Liston, Ali, and maybe a young Frazier.
true, though if rocky were around as long as floyd would he have fought a non boxer and a mediocre contender too
But if there were p4p rankings back then, who of Rocky's opponents would have been on there when he faced them? Moore certainly. Maybe Walcott, but not sure. Charles? Not at that stage. Floyd had something like Corrales, Castillo, Hatton, Marquez, Mosley, Pac, Canelo and Guerrero. And about half of them were actually bigger. Apart from them he had quite a few wins over highly ranked fighters in their own division - from 130 to 154. While I do think Rocky should get credit for beating what there was to beat during the four years he was facing top competition, there is just much more you have to pick apart if you want to take Floyd down.
Charles had lost two of his last four going into the first fight with Rocky, so I have a hard time seeing how he would be p4p ranked. Same with Walcott, but he was at least the undisputed champion when Rocky faced him, so he'd probably make the cut.
Marciano’s best wins are not P4P comparable for the most part. Yes, the names on his list have a higher P4P ranking (in part because the current era has not been fully evaluated yet, and a bias against modern fighters.). Marciano’s best wins (I am not a Rocky detractor by the way) are in his natural weight class, against some (ie Charles) that were not. Whereas Floyd moved up beyond his natural class, and beat naturally larger than himself opponents. HW’s always suffer in this contrast (rightly or wrongly) and Rocky is no different.
