Personally I think that the horsemen should be much stronger, faster, and start with blitz (and probably more promotions as well). They should be practically invincible, but eventually pass away on their own. I think that giving them duration of something 6 or 13 might be nice.
The Balor is supposed to be the infernal berserker as well as an Entropy III Summon and a penalty for the infernal grimorie. It doesn't seem right that a Balor is the weakest berserker on offense and strongest of defense (all others have split offense/defence strength, they don't). I modded this unit to have 4 offensive/ 0 defensive strength + 2 unholy strength +1 fire affinity + 2 entropy affinity. That makes Hyborem's Balors start at close to a normal berserker's strength, but easily become much stronger. Since The Barbarian State counts the mana of all players for its units' affinity, the Infernal Grimorie can be quite risky to build (I also made it provide 1 entropy and 1 mind mana, to make it more valuable)