Which implies that the limits of bone and muscle and sinew and metabolism are different in that world. Follow through in worldbuilding, or shrug and accept that the world is internally incoherent and inconsistent.
Unless it's not -- a fictional world where that's within the range of normal human capacity is conceivable. The question is, if that is possible, how else does that change the fictional world?
Choices:
1) "Non-magical" beast is magical (in the broad sense) and tapping into the same forces that spellcasters tap into.
2) "Non-magical" beast is non-magical.
a) The "laws' of that fictional reality are different such that they allow for this -- follow through in worldbuilding.
b) "They just can do it", there's nothing deeper that actually explains it, and the fictional setting is incoherent.
Dragons are magic.
Mad wizards are magic.
People who can leap over cities or punch mountains down are magic -- or if they're not, you've said something about your fictional world that you need to follow through with, unless you just want "rule of kewl" nonsense.
Nope -- I'm saying you can't have your cake and eat it too. It's not the limits that break verisimilitude, it's the contradictions and incoherences. If human limits with no magic are
x in our world, and 10
x in the fictional world, then you've said something about your fictional world, or you've accepted that your world just makes no sense and you're fine with that.
Note that I've never said "human limits must be real-world realistic in YOUR setting to maintain verisimilitude". I've said "If you change the limits, and don't want to sacrifice verisimilitude, here are your possible solutions".
First, you're assuming a level-based game. This isn't just about D&D-like games.
Second, this isn't about what I want, it's about laying out the inherent contradiction and the mutually exclusive nature of all these things people seem to want.