Try using a defensive tactic. Take a corner, put up your snipers and tower. Build a wall around them. Now stand guard with iron golems, Your taunting orc of enemy hatred, and your fully equipped dwarf dangerous at short distances.
play around with creature buffs, but keep them in the corner. Guarding Golems, and Taunting combined with constant sniper coverage will destroy any frontal assault. Keep the big guys coming (Earth elemental, Golems, Sir Cozian, Talos [if you don't think you can deploy him don't bother trying] and spend some spell book points on other legendaries and incorporeal creatures.
The enemy will not stand a frontal assault. And when you have a DEVASTATING army of pure power (don't waste time on grunts and weaklings).... you. march. muhahaha