Characters with passives tend to be far more powerful than characters without passives in this game. A simple way to alleviate issues with problematic passives is to require a certain number of turns before they activate (perhaps 4 or 5).
This would dramatically slow down the game and should absolutely not be done unless the number of clears required to complete PvE optimally is reduced (perhaps 7 to 4), and the amount of points that can be earned from winning in PvP is increased (from a max of 75 to at least 100).
This change would immediately improve balance across all tiers (especially at the four and five star level). Many currently underpowered characters would suddenly become viable. And we wouldn’t have to worry as much about new characters with crazy passives because we’d always have at least a few turns to deal with them.