The problem isn't the Stoneplate interaction; the problem is Cho has been overbuffed massively.

Q basically has more power than a lot of ultimates, R is one of the best assassination (and objective control!) tools in the game and W is a very powerful trading tool as a silence but it was balanced by the following:

1: high mana cost 2: unreliability 3: Basically only having 3 abilities after laning phase 4: Low damage while building tank 5: Vulnerable when behind due to losing Feast stacks

Everything but 2 was taken out of his kit. Q is 60 mana now (so you can spam it more, AND if you land E it's easier to land the Q W combo). W had its cooldown reduced. E is not only a better ability at 1 point than his old E was a 5 points, but you still don;t even have to skill it because everything you want from it is on rank 1. And now his R damage scales with bonus HP that he gets naturally by way of his kit, so he can still assassinate your squishy even if he just goes ROA into tank (whereas you had a choice between AP and Tank Cho)

I'm not exactly a Cho main but he was my goto mid/top pick for a time, and I said that the E changes would break him, and lo and behold, here we are. Cho had the interaction with Stoneplate before this patch and he was fine. But Cho still had some of his old weaknesses.

Basically take the slow off E, make him lose minion (not champion/epic monster) stacks on death, reduce R's bonus HP ratio, and increase Q's mana cost to 80. You can remove the stoneplate interaction but that is really not the problem with him when he was like sub 48% WR before the E change.