While limiting it so that you can't cast the spells with national mages may be appropriate in some circumstances. Sanguine Heritage, Illwinter, Summon Wraith Consul.

Celestial Soldiers costs 20 Air for 5 Sacred Soldiers, that while strong, takes initially 10 Turns (with TC's income) to make and can't be transformed into a Super Combatant or affect the entire world.

I don't even want to talk about the Celestial Servant. I appreciate him thematically, but he's the farthest from me saying "I got a Celestial Servant by turn 5, phear me!" about.