I really think temporary hp should be depicted as literally ablative; ie, as you take damage it is physically taken off, via a force shield, physical armor, or something else. If it can't be explained that way, I'd rather it used different mechanics, like a higher AC, damage reduction, or more actual hit points. I'm not a fan of "one mechanic fits multiple narratives" if a different mechanic would fit better.
That's D&D in a nutshell though. Look at AC, which is comprised of both "ability to avoid being struck" and "physical protection from harm", which can come from Dexterity, armor, shields, magical effects, racial abilities, class abilities, natural armor, and whatever the heck Monks and Barbarians* are doing to add a secondary ability score to their AC calculations.
Not to mention how my wearing plate armor makes it harder for someone to hit me with a "sustained arc of lightning" (ala
Witch Bolt).
*Oh and Draconic Sorcerers.
Or how narratively there's no fundamental difference between say, bashing damage or fire damage in most circumstances.
Or how every spellcasting class shares some spells, despite the origin and method of acquiring and using said spells can be fundamentally different for each class.
I know, you said you don't like this sort of thing, and would probably wish it was otherwise, but not only would you need to rebuild D&D from the ground up to clear up any confusion, these are ingrained "D&D-isms" that many people would miss if they were gone, and claim the game "doesn't feel like D&D".
And we all remember the last time that happened.