Tbh, i agree with Black knights that the way heroes work is very wrong but i also think the general mathematics rules behind combat in general is wrong and that the trouble with heroes in WoM is deeply tied with that in that regards.
This is what i understand :
-System rules for each attackers if they hit or not with with dodge and accuracy.
-Attackers (each singled out if in a stack) deal up to their attack score in damage +10% or something.
-Defenders (singled if in a stack )ward up to their defense score. Or they ward their defense score and then the attackers get a chance to bypass part or all of the defense score.
Basically. The first set of rolls is and all or nothing. The second set of rolls, considering the relatively low number of HP units have, is also, in most cases, an all or nothing. Granted, with large stacks and high number of units the sheer number of rolls is going to produce some rather stable results (i mean the results of your attacks are around your expectation a little better or a little worse), but where a single units is concerned (namely, a hero) the rolls' results are not stable at all. With luck (and good equipment) a hero can wipe out armies. True. With lack of luck you have a dead champion. Now i get the idea that things are balanced so that a hero matter on the battle field -but- if you ask me there's no way you're gonna have champions who matters which are not ultimates war machines as long as you're gonna have to make them survive through lucky lord's hammer shots, while allowing units with smaller attack score to still do a bit of damage on heavily armored units.
If you ask me what numbers would be needed as for stats effect, equipment, HP of units w/e for this system to be balanced the answer is : i don't know and i even doubt these exists. And to begin with, the first roll is already all or nothing, why the second is as well ?
Now what i don't understand is why the system works this way. Was it to make it simple ? Try balancing it and we'll talk about simplicity. If i wonder about that, it's that there was absolutely NO NEED to be creative when setting combat system.
Take the example of most MMORPG's around here the system is that :
-make one or several rolls for hit/miss/dodge/critical/whatever
-Damage is : Base damage (roll for a random component if any) x (1 - damage absorbtion)
where damage absorbtion is most of the time : Armor / (Armor + constant)
That way the more armor you have, the harder you are to kill, yet, armor alone never completely wards off damages. Thus, the damage are pretty stable. Thus the number of enemies is what stops your hero. Not lucky shots.
Or you can go the Titan Quest way :
Armor deflect either 66% of attack damage or Armor Class, whichever is lower.