Thank you all for the responses... I've learned a lot!
Firstly, from what you're saying, the small game/AI is a big part of it. It sounds like early magic is much more effective against intelligent humans than against giant AI hordes. It's hard to outwit someone who has no wit to begin with
Secondly, my playing style favors mass armies... although I think this is a response to the mass armies the AI likes to hit me with. When you suddenly see 600 troops show up on your doorstep, a pretender or a group of mages will probably get eaten up and spat out... at least, again, in the early game. Meanwhile, my War Minotaurs will happily stomp them flat.
Maybe it's time I tried multiplayer games... where's a good link to get started with that?