It is an abstraction. The representation being somewhat vague and not perfectly working in every conceivable situation doesn’t mean it stops being an representation. And of course HP measurs health (among other things) so this is merely an interpretation, not a house rule.
No, it's a house rule. 5e is pretty clear that it means a multitude of things, including luck, skill, will to continue, and health. If you whittle that down to just physical wellbeing, that's a houserule to edit the rule as presented. I mean, is this controversial? I can very easily say that your houserule really has nothing to do with this argument -- you can go your way or the book's way and the things I'm saying do not change.
As far as it being an abstraction, this is a dodge, because it's being use to discard any consideration of how it works. "Abstraction" isn't a magic word. The reality is that we're using out-of-fiction knowledge to inform in-fiction actions and understanding. In fiction, character A has a wicked gash on their chest. This, unfortunately, does not provide any information on how close to death this person is from, say, repeated attacks from a goblin. Like, if I took the example character A (with a large gash) and character B (with a scratch), we cannot extrapolate at all how many successful attacks from a goblin (1/4 CR 5e version from the MM) each can withstand. The fictional positioning with regards to their wounds has zero predictive or explanatory power. Further, according to the rules, each person will heal their injuries in exactly the same amount of time (this is more a problem with making hp be physical wounds, and usually means additional house rules are in play to mitigate this injury to the fiction). We have no ideas, here, without enabling the out-of-fiction knowledge channel, which is what is usually meant by "meta."
Hitpoints are meta. So far you've evaded my questions or attempted to dismiss them under the banner of "abstraction," as if abstractions are somehow immune to being meta devices (most meta devices you'd complain about are also abstractions). This really seems like you're just staunchly defending hitpoints as being not meta because you don't mind them but you do mind meta, so hitpoints cannot be meta. This is thin rationalization.
It indeed is rather odd that healing more epic people takes more potent magic. One thing I liked about 4e healing surges was that it allowed healing to be proportional to the recipient.
Well, this is completely ignoring what I was talking about/asking in order to make an unrelated comment on how 4e's healing surges were tied to the max hitpoint stat in a way that 5e hit dice are not. That doesn't address the question, either, as I could just as easily ask how many healing surges would be needed to heal each character respectively and it wouldn't change the question at all. Given that your response doesn't connect with the question and raises a topic that doesn't address it at all, one could say this was a
non sequitur.