So... I made some technicians construct a tank base, made archers promote to marksman, upgraded a defence tower (made the colours grey, didn't dare to start something like stone ^-^'), and upgraded an ornithopter into like... a superthopter or something (just modified colours)
Result: AI makes a whole bunch of ornithopters & zepps to take out the tanks (smart AI!), the tanks are hilarious if you make the range huge & HP/movement low, you have to send in scout units (thopters) to be the eyes of the tank.
Next step, a friend of mine is modelling a small wasp-like creature with low attack/defence, but it's pretty quick - a swarm of those will be a good counter-attack for the tanks.
Screenshot: