The strawman exaggeration is that you could be impaled with a spear going through your head, and it wouldn't affect your performance enough to model. Nobody who actually uses the physical model for HP is going to describe damage in such a way - it's all just mild scratches and bruises, or maybe deeper cuts and broken bones - but either way it's physical (and thus observable to the characters).
Which is precisely what I pointed out several posts back*, its all "Disney damage" to coin a phrase. Even worse, no critical wounds, no dramatically interesting injuries whatsoever (even Disney occasionally has the occasional limping character in need of help)....no damage, just cosmetics....oh and that pesky totally metagame doom clock. Certainly nothing about "how bad a shape you're in", but maybe a "how bad does your makeup look".
The characters might be observing it, but they must also be observing that (unlike IRL) these injuries have no impact on their performance. So...if you want to call cosmetics "physical" then I guess go nuts, but then there's this big "no-go" zone of injury in between "Just another scratch" and "Whoops, I'm dying!" In D&D land, no one ever needs an eyepatch**, or crutches, or loses a limb, or limps. Even if you're
Dying***, none of those things can have happened, 'cause you might recover a few HP and then "Presto", you'll need all your capabilities back. (Makes me wonder what purpose
regeneration serves.) I mean, "an arrow to the knee" might put some people out of the adventurer game, but not in D&D!
*although broken bones stretches it. What bones are you breaking that don't affect your performance? I've broken some pretty "minor" bones in my life and been amazed at how much it degrades performance/capacity.
**possible exception for Pirates, if your DM has watched Mythbusters.
***results may vary by edition.