That's an interesting distinction. Out of curiosity, what do you consider XP vs Skill Points vs Tech Points, etc? I always thought them as the same mechanic, but on different meters for different gains (like money and Adam in Bioshock both being currency). I never realized Chrono Trigger didn't have XP. After all, my party was advancing in power after killing things...
CT does have experience, I guess that was bad phrasing. I meant - even if it didn't have XP, you still tech Tech points, which are separate and advance your characters in meaningful ways that do not add HP or defense.
Maybe this'll help?
In general, experience in RPGs is used to increase stats like attack power/HP/defense(/magic power/magic defense), which serve to make the game easier by rewarding you with the ability to survive longer or deal more damage. This lowers the difficulty of existing fights without increasing player skill. It allows you to get past tough or poorly-balanced fights by
investing time into easier fights. Gear in RPGs and MMOs accomplishes a similar function.
My main problem with experience (and gear!) used in this way is that it drastically decreases the difficulty of boss fights, by making a 1-hit kill attack no longer kill you, etc etc. It doesn't require you to change your strategy or learn, just to acquire enough XP(/the right gear) to be able to tank the fight with your existing strategy.*
I'd like to use experience in Indivisible to advance stats that have nothing to do with attack power or defense. You might get a SMALL amount of HP for lots of leveling up, but experience would mostly do things like grant you extra attacks with your current weapon (proficiency), extra speed (faster bar filling), extra meter gain, or lower meter expenditure for meter-using moves.
These things all serve to make battles easier ONLY with application of player skill - you will still die in the same amount of hits and you still deal the same amount of damage per hit, so you need to improve your strategy to make use of the bonuses experience gets you.
It also means that grinding is nowhere near as important, because you won't turn that one-hit kill into a survivable attack - you still have to figure out how to win.
* This is somewhat oversimplified but is true in the vast majority of cases. It's also one of the main reasons I find fighting games to be much more fun than MMOs.
Mini rant:
In fighting games, the characters are static and what improves is your OWN SKILL, whereas in MMOs you get better items and do not have to improve as a player, except for max-level PvP or whatnot, and indeed you CANNOT improve as a player enough to, say, be able to beat the L99 Demon Lord as a Lv1 Farmer.
Fighting games reward you for getting better at the game, and
only that; MMOs reward time spent, and require much of that same time to be spent even if your player skill is already higher than average. I kinda...hate that.
However, the fact that MMOs do indeed NOT REQUIRE much of an increase in player skill if enough time is spent on them...is what makes them so popular with the vast majority of people. And it's what will keep fighting games "niche", no matter how much you simplify inputs or whatever else, because fighting games
require players to increase in skill to progress further. Unfortunately.