I'm not really a fan of how upgrade points and all that work. I think I preferred the first game's leveling system. All I'm finding is that completing those optional Adventure Missions that reward you with an upgrade point end up just basically leaving you with a flashing icon on your menu telling you to spend extra points even though you don't meet the level requirements for any slots you haven't bought yet.
I'm assuming they're gonna end up being used on our other subclasses, but it all just seems like an oddly misguided way of trying to convince the player they have some sort of freedom of choice, when really they're just unlocking things along a linear path as they progress through the story, and being given the option to pick from one of something from a cluster of unlocks.
It makes sense in a game with an actual skill tree where eventually when all is said and done, despite being at the level cap and without any upgrade points, you're not gonna be capable of filling every slot in the tree, like most RPGs do, but eventually we are going to fill every slot, so it seems kind of useless to let us manually pick and choose. They should just unlock automatically as we level up.