Speaking of ultimate banishment, it's a zero fatigue spell. A couple of of pythium divine casters leading a a communion of 8 or more communicants and blasting away at undead hordes with massively powerful banishments is a sight to behold. because banishment doesn't cost any fatigue, a few communicants can easily empower any number of theurgs. (without being killed for a change )
With enough matrices any nation can do that though it's cheapest for Pythium, obviously.
I used this tactics agains Ermor once, and had it used against me a few times, it is extremely powerful against big hordes, though not very effective against SCs. And be prepared to lose the communicants after the fifth round if the battle isn't won by then.