Correct. Just like saying HP is morale or something, they do not translate that way.
From the 2e PHB revised glossary for your perusal.
"Lifeforce" would require touching the ability scores because this is the lifeforce of the character. 0 CON = death. 0 any score = death.
Searching the 2e core rules product there are only 2 places in ALL those books that mention "lifeforce". Spells and magic in the small section on druidical magic, and Accidental or violent death in the complete handbook of elves.
XP is not only what the glossary says, but what it represents. Why do you gain new abilities as you gain a level if it is just your "lifeforce"? Is XP a magical thing, or a mathematical representation of your accumulated knowledge?
Aging one like thw Wraith from Stargate Atlantis, or any other succubus does not really work in D&D, so they figured the easiest way to do it within the rules they created is all.
I mean when you think about what a succubus is it does age people, but if XP is lifeforce and you lose a level, it is really making you younger as you can go through those levels again, so losing/spending XP to make magic items gives a LOT more to the one doing it that you would seem.
Say the person who made 99000 GP worth of items then regain those easy XP with those extra items, and the cycle continues. With XP viewed in this way it is overly powerful and creates an infinite loop within the game to further disrupt the world economy worse than 3rd already did.
So XP represents class skills and knowledge being the reason you gain class abilities from it. It is a metagame concept and should remain there.
You want "lifeforce", look to CON and the other ability scores.
So thanks for trying to help make my position understood, and sorry, I stopped reading when the rules of 3rd appeared in your post as I REALLY want to forget that edition badly, but sure it was good stuff that you wrote about them, and tore them a new one.