Don't get me wrong, I love Alpinia...it's just that Kerria does Alpinia's job better. I predict you'll find that in your debuff squad, if Alpinia usually survives to run out the clock, then she'll pull ahead of Kerria due to counterattack damage. If Alpinia usually doesn't outlast the boss, then Kerria will pull ahead. It's not an issue of which girl is stronger with respect to damage done, but which girl deals more damage simply by surviving the longest.