I haven't played that much but considering game mechanics and orc lack of healing, maybe that could be compensated by giving them some kind of natural regeneration.
Also the talk about armor/damage should take into consideration that magic system was put aside while more important issues are resolved. When you place icon over unit attack number you see all kind of attacks, fire, electricity....I'm sure that some units were planed around those kind of damages/resistances, and with those features not implemented whole system needs redoing.
I do agree about armor resistance being more powerful than damage. Elven grandmasters have high survivability and blade storms seem like a squishy squids i need to replace them after every battle. So i stopped using them.
This could probably be compensated by implementing new kind of stat like "power" that ignores armor buff, say unit A has 50% slashing res and unit B has 10% power, when B attacks A using slashing damage, unit A slashing resistance is reduced to 40%.
Im speaking strictly from elven PVE point of view as i haven't played any other races.