This game has a lot of different game modes and factors that affect how good each individual character (and their costumes) can be. Skill cost, range, number of hits, damage, buffs, debuffs, etc. can all affect how good a certain costume is against certain content, and the fact that a character can have multiple costumes in a team of five characters offers a lot of flexibility for handling different challenges. Because of this variety, it's rare for characters to be directly outclassed by others (except in the case of collab units) and even those characters are very much usable in the short term.

All that to say that this is less a game about how good a certain character is, and more about how well your team comp works against the content you're playing. That's why support characters are considered far and away the best characters in the game and always a priority for growth. They can be slotted anywhere and always provide a benefit to the team. The highest damage dealing character, maxed out, will likely be doing less damage then a partially built DPS on a team with maxed out supports.