Personally, I would prefer all of the abilities to be unlocked from the start, as well as your character being the strongest they possibly can be from the first moment you start playing them. Then when you do start increasing the difficulty, enemies become more difficult through something like adding more attacks & lowering the amount of time you have to react before you get hit instead of just making the numbers bigger (altho bigger is better, as we can all agree (sorry Minori & Ryobi.)) That way it's not the actual character themselves improving, its you, the player, improving.
I would say if they were to add some sort of grind, it would be to unlocking weapons much like DW does it like Mario mentioned above. Then you would have an entirely new set of skills/abilities you the player have to master.
Grinding for cosmetics wouldn't personally matter all that much to me because I find each characters default outfit is kind of part of them & changing it feels like i'm changing them in a way lol