I like your idea, but would like to discuss the CC starting at 50% part, as I think your suggestion would be fine without this part as armour already means nothing from the mid-game onward for yourself and for everyone except bosses. It breaks from 1-2 attacks, as the armour stats doesn't seem to scale as much as our health does (My 2h guy for example had 11k health and 2.5k armour at level 20, it would absorb 1-2 hits). Just lower the armour on the early game enemies, and armour would mean something for the whole game.
Instead I would just make any soft CC, CC that doesn't completely make you lose control of your character (so everything except freezes/stuns/charms/knock-down), not being stopped by armour. All the soft CC like silence, slows/cripples, disarm, etc. feel pretty useless at the moment, as you could just completely shut them down as well.
It might require some enemy updates as a lot of them just run around doing nothing when they can't use their main attacks. A mage often doesn't even bother trying to AA for example. And they don't seem to be really using defensive buffs to remove debuffs.
