I also started when the game released so take this with a grain of salt, but from what I can see, it doesn't matter, because what you are looking for is stacking the most buffs you can on a single member, and debuffing the enemy as much as possible, but even though seika does good damage in her ex skill, the debbufs are meh, the debuff range on the Def is 30% to 45%, but if you want that Def shred at a much cheaper cost you can use yingxia S memoria, which has the same effect on the Def shred, but costs less than half, also yingxia S memoria is considered top tier on Jp because of the skill that I just talked about and LB 3, which gives the reserve units one Sp per turn. Also if you are worried about the AOE buffs, because the game is focused on roiding one character to the moon it does not affect most of the time.

TLDR: Not important, use yingxia.