Current system, Earthquake combo only works if you take the extra step to break physical armor. This means the game winning strat require set-up for it to be used.
Proposed System, multiple Earthquake destroy everything so you can just spam it. Situational and set-up combo turns into "Fire-and-forget" because the limitations all have been removed, just with dice roll slapped on top of them.
If the system is designed without even keeping tactical decisions in mind, why even try to bring it up in a game that is supposed to be about tactic? The game needs more situational combo and viable winning strat, not less of them.
If you want RNG CC back, then it's time to remove majority of the CC from AoE mage tree and make most of CC single-target.