If you want to see what a system like this would look like, there is a mod that does exactly what you ask called "Armor-based saving throws".
Personally I agree with the last two posts in that RNG like this is not the way to go.
In DOS:1 when you fought a boss, or any enemy for that matter, every bit of CC you got off (assuming you didn't save scum) was rewarding but once it wore off you had to find a way to do it again. The first disable you get off on someone doesn't mean the next one will be easier.
In DOS:2, once you get the armor off a boss or any enemy, they become extremely easy to disable again and might as well be dead. The problem as I see it with combat is that after the first turn or two, when all the enemies have had their armor removed, you are really just playing clean up.
I'm experimenting with a change via modding so armor is heavily reduced heavily (50-75%) and restores (50-100%) every turn, so every turn is effectively a fresh slate.
Also attempting to make some damage (50% is my test value) of all damage you deal go straight through to vitality so when the armor is restored you are still capable of dealing damage to the target, and thus overarmored targets don't become effectively invulnerable.
