But Earth has the same "cheater" spell as Town Portal, and Air has incredibly cool Astral Gates; and Haste and Slow, the two most powerful spells in the game (given roughly equal armies and the presence of shooters), belong to Air and Earth.
For a while, I also took all 4 schools of magic, but then I concluded that there are other skills that are just as useful (for example, Logistics, which I think is even cooler than all these magics!). Besides, I prefer playing on small maps and at the highest difficulty level (I mostly play against the AI :(), and as you can imagine, that brings some changes...