Not necessarily.
They're an abstraction, sure, but an abstraction of something very real in the fiction: becoming better at what you do as you continue to do it.
The concept does work much better if one has training-to-level-up rules in place, though, as at that point it maps nicely to almost any repeated training regime in real life. You learn the theory and method in class, go out into the field (or workplace) and put that into practice, then when you've mastered that you come back to the class for the next round of theory and method. I've done this for both work (sales training) and hobby (sailing training when young).
XP are simply an abstraction of your progress in mastering the most recent round of theory-and-method training.
D&D XP raise the same things (based upon your class) no matter what you earn them from. that makes them meta. The gain is immaterial of what it's from. Johnny Runnaway, Morale 3 antihero fighter, gets all his XP from avoiding encounters... but still gains an improvement to hit and more hit points from his XP. Bobby Bellicose gains his XP from actually fighting... but, being a fighter of the same level as johnny, gets exactly the same gains. All very meta.
Likewise, not all AD&D XP are from
Many games XP (or EP, AP, CIP, additional CP, etc.) are even more thoroughly meta - What you choose to raise need not have any relationship to what you've used. Many more, using class and level, may as well be D&D for experience purposes.
GURPS and Hero both allow you to spend the additional Character Points on whatever... buying off disads, increasing skills known (even if unusued)... but many GMs require narrative support. Only if the GM limits advancement to that which has narrative support is it not meta — but the
rules assume the meta mode.
Traveller T4 "Marc Miller's Traveller" - the award of XP is meta - even tho' the XP can only be used to raise a skill you've used in session - because it's for playing the session and/or good roleplay.
The few games where Experience is purely abstraction and not meta tie it to used ability.
- BRP — including RuneQuest — the experience tick is for using the skill. pure abstraction.
- Note that some tie to session, others to adventure, others to character months,
- Burning Wheel (& BE, MG, TB) — Experience ticks are tied to specific abilities and earned by use of those abilities.
- MegaTraveller — Experience is tracked to the specific skill based upon use thereof
- Classic Traveller — specific in character training regimens are needed, and are considerably less effective than Character Generation at adding skills over time.
I've a dozen more less well known ones that do likewise.
Of several hundreds I've read/run.
About half a dozen lack any advancement at all... Yes, there are games with no provisions for character change.