We needed something besides the r-word.
"Realism."
And there
is an alternative to both "realism" and "verisimilitude" which is natural, simple, and fitting, without implying that something must conform to IRL Earth physics/biology/etc., while still recognizing that limits and consistency are important.
"Grounded."
A work, a world, that is
grounded is one that fully earns whatever deviations from reality it offers. It gives a solid, reasonable explanation for its weirdness, or at least assures you that there
is one if the reason is secret/mysterious (often, in part, by taking the consequences of such weirdness very seriously.)
It is not "realism" because there is no real world thing it is imitating. It is not "verisimilitude" because there is no "truth" for it to have similarity to. Instead, this rightly places the locus of concern where it belongs, in the
evaluation of the world, not as an inherent
property of that world. Two people may disagree about whether a world is well-grounded or not. That is perfectly acceptable. The concept does not claim absolute or universal truth.
there is nothing that contradicts it as far as I can tell, and the assumption that a D&D human is what we know as a human (Homo Sapiens) seems pretty reasonable too
When you are bringing in limits and denying that something can be done or allowed, the burden of proof is on you. "It isn't contradicted by the text" isn't enough. "It is reasonable" isn't enough...and, as far as I'm concerned, it
isn't reasonable. A typical town guard is like level 2ish, and can survive all but the worst 20' falls with no serious injuries, and most 30' falls, since they have 11 HP. As long as there's someone at the bottom to stabilize them, they very frequently survive a full 50' fall and be right as rain the next morning.
That's objective. Baked straight into the rules. Falling is 1d6 per 10'. Town guards have 2d8+2 HP, static 11. Instant death only occurs at -100%, which would be 22 total HP. 5d6>21 only 15.2% of the time. Even a 60' fall is still more survivable than not (45.36% chance of instant death.) IRL humans, even in safety equipment, die from falls as short as six feet, and have fatality rates on the order of 30% or more from falls as short as 20'.
What supports the idea that commoners are different?
See above. We shouldn't assume either way. If you want to assert that essentially all IRL human limitations apply to human commoners,
you need more. The burden of proof is on
you, not on someone saying, "hey, hold your horses, we can't assume their limits are the same as ours."