Sheep is a great overpower
Callback can be limited to 1 use per battle or recharge rate should be about 3-4 turns. Demon-specific gift...you can make it so that it won't end Archdemon's turn if you think it's too weak
btw Archdemons aren't as weak as you say:
* auto-dispell
* "unlimited" speed
* fire resists
* not bad Attack
* u gave them aoe fire-attack
* u gave them demon summoning ability
so the 3rd ability should be not so strong
or their leadership should be increased