Pfft. If you're looking for an RTS with demon summoning, you have got to try Warrior Kings. Seriously. Abaddon kicks flippin' A.
Mind you, that game had some MAJOR control issues that would cause me to rip my hair out if I ever tried to play it without the cheats. The computer players, being the stupid jerks that they were, would of course be able to completely circumvent these issues. You? Not so lucky.
Your villagers wouldn't even be able to tell if they were on fire or not. With the (almost mandatory) invincibility cheat, your entire city could eventually be turned into a raging inferno that belched an entire atmosphere of smoke and fire into the air. Does this remind you of anything?
The demo lets you play as the pagans, who are the demon summoners. Try it out. Also, if you're trying to do things the "honest" way, here's how to win with the pagans...
Step one: Summon a member of the gibbering horde.
Step two: Tell it to devour a tree.
Step three: Go do something else and forget about the hordelings munching down the nearby forest. By the time you get back, there will be enough of them to kill your CPU. The enemy player will be child's play.