I actually really like the idea that sure keep magic and physical armour separate but shattering one removes the other completely making the target vulnerable to any source of CC.
This would give mix dmg parties an advantage again, promote proper target selection, and still allow for defensive specialization.
If you have enemies that are stacking a lot of physical armour but have less magic protection you use your mages to focus them down till their armour is shattered then move in with your physical dmg dealers, or the reverse.
You can still rock single type dmg parties but some fights will be harder for you because you wouldn't be able to target their weak defense type.
I don't know this is the only idea that I feel still accomplishes their goal of making perma-CC harder from the start of battles while still allowing for build\party diversity.
