Is having that level of motivation/dedication not just a natural ability/advantage in the same way that superior reach or speed is? In this ense you could be asking who would've been better if only they'd had more power, etc? I'll throw Deontay Wilder in here. He's got plenty of physical advantages over most guys even at heavy - he's tall, fast, packs power and has long reach... If he'd had the dedication to learn some technical skills, develop better fundamentals and not skip his leg days he could've been orders of magnitude more dangerous - if he'd had the dedication to build his resume (instead of being the ducking king at HW) as well that would be nice.
Young Griffo or Nipper Pat Daly. Griffo was taking people like prime Gans to draws whilst being drunk, outsized and pot-bellied. He even taunted Gans and told him not to hit his stomach, but when Gans went for it he avoided every blow. Pat Daley went pro at 11, was sparring with Mickey Walker at 14 and was a world ranker with wins over top euro champs at 15. Absolutely disgusting how he was mismanaged so young. He would've easily been Britain's best ever and a p4p top fighter imo.
I don't understand how a guy can win world titles at 160, 168, cruiserweight and heavyweight and be an under achiever. What else should he have done? Write a novel? Cure cancer? Keep in mind that if he had stayed at one weight, the "hardcore" fans would say he under achieved by not moving up in weight to challenge himself.
You don't develop that kind of skill being lazy and it isn't natural. It comes from thousands of rounds of sparring and work. What people may not know about James Toney is that his moving up in weight was not due to him being lazy. He did it on purpose. Back in the early 90s he did an interview with a boxing magazine in which he talked about being heavyweight champion, about how heavyweights were too slow and not smart enough to handle his style.
Sonny Liston was an alcoholic, probably, while champion. Carlos Monzon smoked many cigarettes in a day. But, without meaning to sound too wank, the right answer is Young Griffo. Griffo was an Australian bantamweight who bloated to lightweight with peeve and disinterest who fought Gans to a couple of draws, could fight guys like Dixon and Erne and Lavigne at that weight without losing but without really trying to win. He just sort of turned up and didn't get beat up because he was a defensive genius, but didn't really try that hard. He boxed mainly draws in an era where aggression was prized enormously. But he didn't fight aggressively. He just didn't get hit while tossing featherfisted no power punches. It was all a jape. If he had the discipline of Bernard Hopkins he very likely would have joined Sam Langford and Bob Fitzsimmons as an elite pound for pounder. At a guess.
i remember reading in the boxing rags how he was said to have been falling down drunk the night before some big fights. another of his countryman i think could have been atg, at least of his division, was jose luis lopez. but he loved the surfer, stoner life too much too.
If James Toney had trained like Floyd Mayweather, he would have been one of THE all time greats. But Toney loves his food and loved to just brawl in the gym.