Interesting. I've only been following this very casually, but I have a question. Was the recent fight by boxing rules or MMA rules? If the former, would the MMA fighter (McGregor?) have fared better or perhaps won if MMA rules had prevailed?
To add to what BCC said, it makes a huge difference that the fight was fought using boxing rules and not MMA rules. It's a completely different skill set. The special skills that make Mayweather one of the greatest boxers ever aren't very useful in an MMA fight. The punching is the same, but the defense is completely different.
You could stand right in front of a professional boxer and throw punches at him all night, and not hit him once. He could dodge or duck or deflect or block every punch you tried. It's an impressive skill. But it's all based on the idea that you're only allowed to hit your opponent's head and upper torso in boxing. The boxer doesn't have to worry about being kicked in the leg, or grabbed, or taken off his feet, because none of that is allowed in boxing.
Boxers and MMA fighters stand differently and move their feet differently. MMA fighters have to stand in a way that they are ready to defend against being kicked in the legs, or being grabbed by the legs and taken to the mat. Boxers stand in a way that promotes upper body mobility. They fight tall, with their hands high, and it doesn't matter if their legs are vulnerable, because their opponent can't attack their legs.
An MMA fighter will usually use a lower, wider stance and be ready to get their torso low if their opponent closes in, because they might need to defend against being taken to the mat, or conversely because they might want to grab their opponent's legs and attempt a takedown. If a boxer tried to use a traditional boxing stance and boxing footwork in an MMA fight he would be very vulnerable to being taken to the mat.
The finer points of boxing artistry-- head feints, ducking and weaving and all of that sort of thing-- don't really protect you if your opponent wraps your legs up and drives you against the fence. However, good boxing technique is still a big asset for an MMA fighter, because every MMA fight starts standing up, and if you don't know how to defend yourself against someone who can strike well, you can get knocked out. Some MMA fighters, like Chuck Liddell, had very successful careers by combining the ability to punch really well with the ability to defend against being taken off their feet.
Ex-boxing champ James Toney tried to fight ex-MMA champ Randy Couture in an MMA fight. Toney was confident he could just knock Couture out. Couture was much smaller and much older than Toney. In the opening seconds of the fight, Couture simply caught one of Toney's legs and yanked him off his feet, and Toney had no idea how to protect himself when he wasn't standing up. Randy easily manhandled him on the ground until he had Toney in a "sleeper" hold, and Toney went unconscious. The fight only lasted a couple of minutes and Toney didn't get to throw a single punch. If Toney did have a chance to land a punch he probably would have knocked Couture into retirement, or orbit, or both... but he simply wasn't able to stay on his feet long enough to do it.
One boxer who has had success in MMA is Holly Holm, who had a very successful boxing career before moving into MMA. But she was also a kick-boxer, and so she is very comfortable with using a variety of different footwork and striking techniques. As well she has trained very hard with MMA coaches to learn to protect herself against being taken off her feet, and she is extremely good at that. People remember that Holly beat Ronda Rousey using a kickboxing-style kick to the head, but she had actually beaten Ronda up for 2 straight rounds using mostly boxing, until Ronda was so tired and dazed that she was a sitting duck for the knock-out kick.
So boxing is a great tool for MMA fighters to have, but it can't be your only tool in MMA, or you end up looking like James Toney.
-k