With respect, I think the “most games don’t do this” argument is not especially helpful. You only have to say the same thing, phrased differently, to offer the counter view: some games do.
Battleborn attracts many different kinds of gamers who have different expectations. With its loot, chests, PVE “dungeon” grind, character levels, and lore, it draws in a particular kind of player who is accustomed to - expects - that a level cap is not the end. MMO and Diablo-clone players are used to alternate advancements beyond level, increasingly focused and rewarding grinds, a continually raising endgame cap. In those genres, what you describe as an unreasonable exception is the norm.
And Battleborn knowingly, deliberately flirts with those genres and appeals to its fans.
Because Battleborn is designed to attract grind-gamers by having loot, bosses, and repeatable missions: it is only reasonable that grind-gamers be allowed to voice what they would like to see accentuated from that element of the game. It isn’t fair to criticize anyone for not having chosen (for example) their personal goal to be the mastering of the entire cast. Many RPG/MMO players choose a single class or character, identify with it, and want to go as deep as they can without changing. It’s not shortsighted of them: it’s just another way of enjoying games.
For every kind of badass. That’s the motto. Worth remembering.