[Vynd]

I think that SCs are better than armies of mages at pretty much any stage of the game. But it's not like the two are mutually exclusive. If you want to do well, I suggest you aim for as many SCs as you can get, and plenty of mages too. The SCs mostly require gems to summon and equip, the mages mostly require money, so there's no reason you can't have both.

There are other spells besides Banefire and Gifts from Heaven that I would worry about late in the game (although I'd certainly worry about those). Long before the end game I could have an army of level 1 Water mages casting Quickness and then cast Frozen Heart over an over again. That ought to make an impression. If I was C'Tis or Ermor I might go for hordes of Life Draining mages.

So the points is, there are options beyond Fire and Lightning. And if we're seriously talking about a situation where I've researched everything (something I've never even come close to, although I'm sure it's been done), well then if you've any sort of variety in your supply of mages then you ought to be able to find something your enemy isn't prepared for.