My opinion is that you can't even begin to compare boxing to mma directly, because there's so much more involved. That's no fallacy. You want to compare the best of our generation in Floyd to, what, exactly? We see fights regularly where a fighter has a "go to" style or technique, and still pulls it off time and again. Cruz, Maia, Khabib, Cerrone, Barboza, Jones, Rampage, Rashad, Anderson, Leben, Wanderlei, Fitch, Okami, Shieds, Hughes, etc etc etc. It's never really been a secret as to what any of those guys were going to try to do in a fight, but being able to impose ones self on their opponents is simply the mark of a great fighter.
You're presenting opinion as though it's fact. Of course boxers have better boxing than mma fighters, that's all they train! In other news, soccer players are better at Soccer than basketball players.