"HP" "Levels Period"
Those D&D mechanics have always been quite meta. Like, why do you suddenly gain this big chunk of class abilities all at once, etc?
Yes you can tolerate them because of other things the system does that you like, or simply not care, but that's hardly the only option. Shadowrun, GURPS, and Mythras require substantially less contortion to 'explain' what's going on (though they do offer the more D&D type XP options as well, the granularity of picking up new abilities one at a time is a valid design choice, and so is not having JRPG style rapidly ballooning HP pools - GURPS also has learning through training. Levels, rather arbitrary XP, and quickly accelerating HP pools are not the only option).