Yes. AC and HP are abstract. They don’t represent one specific thing, but they can represent any specific thing that suits the fiction.
I agree that they're abstract, but I'm of the opinion that the problems come in when they try to represent more than one thing at the same time.
As I noted before, hit points are a prime example of this. Ask most people who don't have a background playing D&D what an instance of their character losing hit points represents, and 99% of the time (or more) they'll say something to the effect of "the/my character is taking damage." What they
won't say is "they're getting tired/running out of stamina."
There's nothing wrong with wanting to model exhaustion and fatigue in terms of a depleting pool of points that requires resource management. But having it do double-duty, i.e. having the
same pool of points also measure how much injury you can withstand before your life is in danger, is a mixing of concepts that tends to be unpalatable for a lot of people, because it invites conflating two things which aren't the same (even if you can make the case that they're related).
Armor Class has the same problem, in that it combines "avoiding the attack entirely" with "receiving the attack in a way that no injury is dealt." That's what I liked about 3E's use of "touch AC" (representing dodging the attack altogether) and "flat-footed AC" (tanking the hit without being hurt), even if the latter had overlap with damage reduction. That AC bonuses were themselves listed as discrete modifiers, with the bonus types at least
suggesting what they did from an in-character point of view, was an added bonus (see what I did there?). A monster having a "natural armor" bonus is flat-out said in the DMG to be "...the type of bonus that many monsters get because of their tough or scaly hides," and which is explicitly said not to add to flat-footed AC.
Does a given monster's natural armor bonus exceed what a magic suit of plate mail has? Sure, but that just tells you that the monster's hide is tougher than even magic plate mail. Which is fine; some monsters are just that tough. Can you make a suit of armor out of their hide that has corresponding toughness? If not, that's likely due to some aspect of the hide being lost in the collection or preparation of their carcass; coming up with a verisimilitudinous explanation isn't that hard, even if it is a gap in the rules.
To be as clear as possible, this is all a matter of personal preference and opinion; no one is saying anyone else is right or wrong. But I don't think it's an unpopular opinion among gamers to say that verisimilitude, i.e. where the rules tell us what's happening in the game world, and why/how it happens, can be impinged when those rules move away from that in-character explanation, which is what happens when you start putting multiple, disparate representations of what's happening onto the same set of mechanics.