I have a warrior , on hard , and just made it to the labyrinth. At first it was difficult for me to in Demonis too but I find the game balanced since the are counter troops for every enemy you find for ex. you can use demons against dragons or a combination of unicorns(both)/undead or dwarfs/undead(most important vampires) plus trap and the spell that makes a unit unable to use abilities ,forgot it's name .. spell shakle i think.
What pisses me off is that in my game haas's incarnations have few dragons and that makes my demon army not so imba