The topic of Martial Artists is a little unwieldy to use as an example because our primary point of evidence is Ranma 1/2, and there is explicitly a significant amount of magic in that setting. People like Kuno and Akane who have lived in mundane suburbia are evidently weaker than other characters; whereas most of the strongest characters are either a) wanderers who have been exposed to powerful magics like Jusenkyo or b) Amazons who live nearby multiple sources of magic and keep powerful niche artifacts as tchotchkes.
It takes no changes to the setting to conclude magic exposure might account for some of the weird martial arts BS.
I'm not saying magic exposure doesn't make you stronger, I'm saying that you can train ki in a very mundane environment and still gain physical superpowers fully competitive with what
typical mages get just passively from having magic in their anatomy and metabolism.
I doubt that the average Silver Millennium human being who just walked around doing normal stuff and made no special effort to give themselves a workout or learn combat magics or anything was stronger than, say, Akane.
It's more the insane dedication needed in this environment yo get to the NWC levels.
Quite true, though the Nerima Wrecking Crew are also major success stories.
The reason I originally brought this up is that because this is a world where there exist dedicated forms of training that
do in fact give you superpowers, the Masquerade almost certainly includes some degree of people just rationalizing that. We fundamentally accept that yes, if you train hard you can karate chop your way through a plank. Even though it seems implausible at first glance, well, the facts speak for themselves.
It may well be received wisdom in this setting, even with the Masquerade in place, that some weirdos can dead-lift a compact car or shrug off being beaten with baseball bats or something, just because that's empirically true and you don't even have to be a fully conscious ki user to get there. The limits of what a 'merely athletic' person can do may well outpace what an athletic person
without actual ki manipulation but
with spellcasting ability passively gets from their mana.
The more blatantly magical stuff like elemental manipulating ki techniques is probably kept hushed and not discussed, under Masquerade. But the physical side, or at least some of it, is probably too common to fully suppress.