Hello,
@offwidth
@Kozushi is right. They are perfectly fit for boxing (fast, smooth, have endurance, etc...) because their body have been naturally adapting to this kind of effort. But I do not believe they actually need to be able to perform these push ups, which is something I saw during warm-ups.
In terms of pure fitness, this is always curious to notice that in the locker room, some of those "boxing-fit" / "fighting-fit" guys are either pretty skinny (without even really visible abs but visible ribcage, like Sean O'Malley or Max Holloway), or almost "fat" like Daniel Cormier).
I should mention that different combat sports or martial arts require different training regimens. For instance,
@Kozushi will certainly benefits far more from doing TGU to perform judo than I'll do for boxing. The reverse remains true, at least to a certain extent: maybe I'll benefit more doing clap push ups for boxing than him. In both cases, performing the two remains the best option if one aims to get a "complete" GPP.
Plus, we also have to consider the difference between the "daily routine" and the "pre-fight" routine in the camp.
Here are some training routines (but I guess they have to be taken with a pinch of salt):
Carl Froch's routine:
Carl Froch's Boxing Workout
Pacquiao's routine:
Manny Pacquiao Training Camp Analysis - Boxing Science
Anyway, here is just to link to realize how many training methods there are, depending on the fighting style, preferences, etc...
Fitness Archives - Evolve Daily
Among them, here is an interesting one:
According To This World Champion, Here's How To Work Out Effectively In Just 30 Minutes - Evolve Daily
Kind regards,
Pet'