Originally Posted by Saertis

It just doesn't have any sense. If girl with single target skill can finish enemy by herself then she won't use her full potential (deal all dmg she's able to) if aoe girl weaken enemy she'll attack. Either way one of them won't be using her full potential. However if girl with single target skill would be after aoe girl then it can happen she'll use her skill on almost dead enemy.

I can think of a contrived situation where it would be useful to have AOE first. If your AOE girl and your single target girl can both take out a target, it's better to have your AOE go first so that your single target can hit another enemy. Otherwise, your single target hits the enemy which would have been eliminated by the AOE anyways.