As I say, maybe cc should work before both armours are zero and the armours could be exchanged when another one is zero.
I believe this way solves your argument and keeps the design spirit.
Forget about CC. I'm talking about dealing damage to vitality. Only salvation for my case is making a single CC shield that would decrease simultaneously with damaging vitality. Maybe add some special spells for reducing exactly that shield without vitality damage so you got choise - try kill fast or try to CC faster. It would solve CC problem leaving concept of anti-CC shield in game but allows effective mag\physic damage dealers cooperation.