I may not have any PTR experience but the choice is simple. We all know that Wrath fights are all about big damage. So you have to ask yourself to you want something on chance or that will be there no matter what. If gemmed complete avoidence on your ToC gear and enter a cold streak on dodge/parry you better have one good healer backing you as your health percentage will drop hard.
Now it seems to me you can either try to explain but it seems hes a stubborn individual if you came here. I can only say that you either do as he tells you or he'll bench you like he has. Some GMs get a god complex of i know a special secret and if you dont play ball ill bench you no matter how good you are. Really it depends if you like where they are in progression and if you are comfortable of finding a guild at the same level of progression.