Now, i checked and didn't see this posted already, and i figured if it is it's piled underneath pages of useless junk.
Anyway, as a priest you can easily break any polymorph on you if you follow these steps.
1. get an enemy castbar mod so that you can see if someone around you is targetting you and casting poly.
2. wait til its right about to cast and then shadow word: death someone. as long as it doesnt kill your target, it will hit you back for damage After the polymorph hits you, causing it to break.
this can work on other cc thats breakable by dmg if you can predict them and time it right.