I can speak on Mayweather with confidence as I used to be a huge boxing fan and watched every single one of his fights live since he faught Henry Bruselles while giving his opinions of the upcoming football game Jim Lampley was discussing. (he rightly predicted the Patriots LOL look it up he literally is in the middle of a professional boxing match commenting on what Lampley and Merchant were talking about ringside as the fight commentators. It was unreal, thats when I knew he was something ...different.)
That was when his nickname was Pretty Boy Floyd and he was knocking guys out. He was a sportscenter backstory highlight at the time getting almost zero exposure. Shane Mosely, Tito Trinidad and a few others were at their peak during this stage, them and DeLaHoya were getting the big money fights.
Floyd just kept quietly winning and building his brand. After knocking out Ricky Hatton in 2007 his career finally took off. He moved up in weight, dtopped the Pretty Boy handle and became "Money May".
Leonard Ellerbe and Al Haymon started to really leverage his star power, using his undefeated record as their life-raft argument and just putting a mic in front of him. He talked more shit than anybody since Ali. The media and public hated him for the most part and he started to embrace the villian role. He would even claim patriotism when needed to sell a fight.
He silenced all of his critics though when he added the scalps of,
Juan Manuel Marquez
DeLaHoya
Miguel Cotto
Canelo Alvarez
Maidana (twice)
Manny Pacquiao
And this is after he had already beat Mosley, Judah, Gatti, Deigo Corrales and Jose Luis Castillo (twice).
The guys resume is unassailable. He is the best defensive pugulist in history. He is one of the best counter punchers of all time. His ring command is legendary, people dont talk about this enough, he can cut off the ring and reduce an athletic stick and mover to a hopeless brawler. He can navigate the perimeters of the ring himself if he wants and can frustrate and evade the most determined seek and destroyers. Or hell just sit in a phone booth with you (watch Canelo fight) and go toe to toe without taking ANY damage.
Canelo Alvarez would brutalize Connor McGregor. He is bigger, stronger, more powerful puncher, and an intelligent boxer. Connor would have zero chance to beat him in a boxing match. He would probably get knocked out.
Floyd DESTROYED Canelo. McGregor doesnt have a fucking chance in hell against Mayweather. Floyd will probably be an asshole and just demoralize him by doing that little straight jab to the stomach that he does over and over. No one talks about it but its an effective punch that scores points and saps his opponents energy and forces them to start to tuck their shoulders in to defend against it after it starts to land. Thats when hell start to open up with those ear hooks and lead right hands and McGregor will be out of the fight before the end of the 4th round.
Floyd might get a TKO honestly because McGregor is going to be SUPER GASSED by the 11th round. Theres no fucking way that guy is going to take rounds and rounds of punishment and be able to make it out of the championship rounds. I wouldnt be surprised if they throw in the towel in the 11th or 12th because Connor wont quit.