@WavelengthAs for Persona5, I don't know about you but every time I did a plot dungeon I got about 5 level ups or more for everyone in one trip. Now if those had all given me full HP/SP restores on top of that, restoratives would be either meaningless, or it would be easy to complete the dungeon in one trip. In fact, most dungeons already can be done in one trip if you are careful on the current system, the only one I had trouble with on this was the first dungeon as your starting SP pool is just pathetic.
Were we playing the same
Persona 5? I'm only three dungeons in, but in every single one so far, I've been
forced to leave the Metaverse at certain points because X or Y wouldn't open up yet, meaning that I had to make at least three trips to beat each dungeon (and therefore, even if I might gain 5 levels per dungeon, I'd only gain one or two per character on each run).
I do have to agree with you that even at P5's pace, the balance would definitely be shifted significantly by full heals on Level Ups. However, if Level Ups were half as common in that game (and gave you twice the stats/access to new Personas), that would probably be enough to make it a welcome mechanic rather than a balance-breaker. You'd still want to leave the dungeon and rest up before tough mini-bosses or bosses.
In all honestly, I think for HP/SP full restore to work well level ups need to be really rare. Like say Gold Box rare, where you might start the game at level 1 and end at level 6.
I don't think it needs to be
that rare! If it's happening an average of once per dungeon per character, I think that's a pretty reasonable frequency to trigger the full-heal.
Actually, thinking about it some more, we both sort of missed the differentiation between chronic-difficulty (resource depletion) systems that use
Items as the limited resource you're going to exhaust, versus chronic-difficulty systems that use
HP and/or MP as the resource that is consistently exhausted (with very little ability to refill them using Items).
If a limited stock of Items is the limiter, essentially you might go into a dungeon being able to run through your HP/MP three or four times before you're out of points and out of items. In such a game, the Full Heal happening once or twice per character isn't a huge balance-breaking game-changer. In games where you're only supposed to have enough HP/MP to run through the dungeon when skillfully played, and you don't have a supply of Items to restore you a little throughout, then one or two Full Heals per character would definitely break the balance.
Persona is sort of in the middle of that, with a lot of Items to restore HP while MP restoration items are uncommon. I do feel like halving the level-up frequency would be enough to allow full heals (as I mentioned above), but I'm not 100% confident in my read.