I suck with Pythium ... please help!

[Huzurdaddi]

Or is it truely that problematic that simply adding relief casters doesn't suffice?

No number of releif casters will buy you more than 5 turns extra. On the 6th turn they will stop casting releif. I have never seen them cast it after that point. I'm sure someone, somewhere, has seen it but I never have. So don't count on it. You *need* to get the battle over with ASAP with communion. Script the most punch spells even if they take a lot of fatigue ( thunderstike is one that comes to mind ) since time is your enemy not the guys with pointy sticks on the other side of the field.