[CogDissident]

Additionally, you could prepare a strong ground force, spearmen (longer weapons will repell the demon attacks) mixed 1-to-1 with something with a strong melee, and have two mages with them casting an armor buff and fire-resist buff (or one mage, if you've got someone strong enough to do the earth spell "skin of gold", which does both). They'll fly to you and get ripped apart by a sufficiently strong force that knows what they're up against, but you'd need a good 500-600 human troops to do so.

I'm used to playing Ulm or Man, and throwing a million troops at a problem is usually my playstyle, because hey, people are cheap. And a properly buffed army of 100 cheapo units can take out an unbuffed army of 100 giants.