Top elite fighters of today train for so much longer time and have te benefits of many things that were not very available back then like review tapes and more scientifically formulated food intakes. Many top fighters in the past fight every 2 weeks or so. That alone should give us an idea of the kind of preparation they are undegoing. And one intangble thing that makes a lot of difference is that fighters today learn from the fighters before (or their trainers), they study their styles, adopt an make intelligent adjustments.
Where do we get these people from? For **** sake. 01. Tua is so over-rated. Having power and a good chin doesn't automatically mean you beat greats. He got outslugged by Ibeabuchi, and was out-boxed by Chris Byrd aswell as Hasim Rahman, and dropped by Rahman and Barrett. He can't hold a candle to Joe in terms of overall skill. Frazier TKO Tua. Easy nights work. 02. Arreola has no skill other than a half decent jab. Adamek is more skilled, but woefully undersized at heavyweight, can't punch at the weight nor take a heavyweight dig. Johnson is one of the most skilled heavyweights ever, especially defensively. His chin wasn't that bad, he can hit when he needs to [though maybe not against super-heavies like Arreola] and he's very strong in the clinch. Johnson TKO Arreola and Adamek. Easy nights work. 03. Margarito would be completely outboxed by Floyd. He was getting handily outboxed by Cotto before his punchers [possibly with the addition of a certain illegal substance] took there toll against a guy who struggles to go 12 at a pace anyway. If Cotto was outboxed Margarito, what do you think Floyd - quicker, more skilled, smarter and more adaptable and far better defensively and more disciplined - would do? Floyd UD Margarito, winning at least 11 rounds.
Judah doesn't have the mentality of somebody like Pacquiao, not stamina. You think they haven't worked on his stamina in the past? Sure he might gas, but not after 4 rounds. You just can't change his mentality and he's not particularly adaptable and struggles to make adjustments.
To be truthful I think Mayweather would just potshot to a win. But I wont rule Margo out. Margarito got the chin and pressure to cause Mayweather problems for 12 rounds straight.