In terms of overall MMA skills, Punk-Gall wasn't that big of a mismatch. There's a reason Gall shot for an immediate takedown and that's because Punk had a significant edge in the striking department. Punk, while having the ground skills, simply wasn't prepared for a panic wrestler. He showed up for a proper fight and the other guy didn't.
Mayweather is facing a guy whose basic boxing qualifications are that he used to take a weekly hour class at his local gym to try and fend off the bullies who used to torment him, all the while trying and failing miserably to make it in a true elite sport like football. It's debatable whether he could beat Mayweather Sr, much less Jr.