Do you intend to keep Shana/Miranda as the main magic thrower for the course of the game? I think that would be the right call, she gets the highest MAT by a fair margin and Meru's party-wide healing probably won't be as important in a TAS. I suppose dual-magic or dual-physical users might even be worth it in some cases, provided they don't steal too much exp from the end party.
There's a very useful guide up on GameFAQs containing enemy and character info, if you haven't looked at it yet (
link). I'd been wondering if it wouldn't be worthwhile to fight the Polter Armor at some point for the Soul Eater + some exp, but according to this Loner Knights have a chance to drop it without the detour. In that case I'd be very surprised if the boost it gives Dart doesn't save time, even if only because of how
long that final battle is.