[Taqwus]

Tien Chi gets breadth indeed. If you can make your way to Staves of Elemental Mastery (+1 air/earth/fire/water) or Rings of Sorcery (+1 nature/death/astral/blood) or Wizardry (+1 elemental, +1 sorcery as well... but expensive) they can be quite formidable mages.
You do still need to worry about things like Magic Duel, however; a powerful astral mage could threaten Celestial Masters since every CM starts with (low) astral. A Banner of the Northern Star would help.