[Master Shake]

My experience is that SC units are vulnerable to single-target spells like Petrify (a sucessful resist versus petrify mean that SC is paralyzed) or Soul Slay. They CAN be debuffed with things like armor-destroying spells. For SC with very high protection, get some units (e.g. trolls) with very high strength. 25 protection is near invulnerability against 10-strength unit, but not so hot against a 22-strength unit.

Sure, this is not the army-army encounters you are looking for, but that is what I like about the game - there are many different stragtegies and counters. Plus, SC cannot hold territory very well, or pillage, or take castles. Also, drop a couple of your enemies SC (each with half-dozen expensive items) with a couple level 3 astral mages casting soul slay, and he may start thinking about another strategy.