Roberto Duran doesn't strike me as somebody who would just wipe the floor with Mayweather as everybody says. He looked awful when he was stopped by Leonard (apparently there was multiple reasons as to why this was).
Muhammad Ali was beaten fairly several times and I believe 6ft9 Fury would have beaten Ali and everybody Ali was beaten by.
George Foreman was big but if he's the hardest hitting monster, he literally lost to a punching bag against the ropes when he fought Ali. That is not a dig at Ali because we all know he can box, it's just odd to me how Foreman is rated as fearsome as well as a great boxer when if Ali was to stand still against the ropes against Anthony Joshua or Mike Tyson he would get knocked out.
Sugar Ray Leonard used his feet well and had fast hands but his defence isn't comparable to Mayweather IMO, Mayweather had a very tight philly shell defence whereas Leonard was more open and used head movement and traded punches and usually got the better with his speed and feet. In these exchanges his hands would often be down though, Mayweather keeps everything tight and flawless similar to Canelo. I will concede however that Mayweather isn't the GOAT and Canelo actually impresses me more. Mayweather had some very close fights, he was slick but Canelo is immaculate going forward and defensively and he could and would take on anyone in the sport up to 168 and beat them. Mayweather didn't always fight the best.
IMO RJJ is the GOAT.
Calzaghe is also extremely good, however I believe he is wild and would get countered trying to land that volume against somebody like Canelo.
I just find it hard to believe when the absolute pinnacle of boxing today in Canelo Alvarez will just be beaten one sidedly by some of these greats. Canelo's resume is very impressive and his only loss he didn't have a chance. I do think Canelos biggest floor is his feet but he's beaten guys like Amir Khan and Danny Jacobs. If anybody slows down, Canelo has the best defence in the pocket and amazing shot variety - he went up and beat Golovkin in the second by refusing to take steps back against the supposed most feared boxer at the time who was as we know a very decorated champion with an extensive amateur background from a weight above. It would not surprise me for Leonard to beat Canelo but if somebody was to one sidedly put a beating on Canelo you'd have to be almost unbeatable as he is immaculate.
Feel free to dispute any of my points.