Everybody talking about power, damage, usefullness stuff but no harem collection. Even for that i'd get all tp units. And i wanted to add spica aw to +1, without her spirit rescue X can be a mess with just other units, dunno if your aw rita can one-shot them tho.
Well most ppl already explained the stuff, i just wanted to point a different thing.
Another thing is i dont think bernice is that easy to get, i had even better luck getting sophies but not her in 8 months of playing i just get one and even that was from a reroll account, so there is nothing wrong with OP imo. If you have memento and leanne, you dont really need more for tanking except if elvas style suits you and want to invest to her. One of our next events is a HA, offensive one but her stats are good if not like gellius or deine.