Just for anyone that's interested in the difficulty of proving grounds on ptr (This is as a resto druid).
Bronze = Healing For babies
Silver = Healing for babies
Gold = Healing for babies (Apart from the last round which is not really hard but it kind of surprises you after 20 waves of nothing)
Endless ramps it up slightly but not really that much until wave 5 or so. Then it gets slightly harder in that you actually have to pay attention and can't be slow on any despells or the the tanks HP.
Then at Rank 7 it goes to ridiculous mode spawning three casters that will cast fire randomly onto the ground and if your slow to move or stand in it you lose 40% hp. They also cast pyro blast that hits for 1/3 of your HP. As far as I can tell they have no agro threshold and will free cast on your raid after your rogue/mage buddy use there interrupts. They are immune to all cc except stuns as well.
So if all 3 decide to target a certain player they will get one shot and if one of your semi derpy buddies gets hit by the ground effect they will also almost get insta killed by a pyro blast straight after. Its pretty ridiculously RNG and it doesn't help that sometimes your team will dps better and so clear the previous wave faster and sometimes they don't. T
I never passed rank 8 because I either wiped before hand or was ridiculously oom from the previous. It may be easier for or a disc/pally with absorbs. The whole thing is pretty badly tuned going for snorefest to semi engaging to ridiculous in one wave.
If anyone got to rank 9 I would be interested to know how and as what class!