Well, i just recently got past what your up too so what i will tell you this, re spec until you find something that works, that is what i do. anyways, really, all i did was use traumatize onto the sniper whenever he has his two buffs. the sniper should e your first target since he can one hit kill anyone of your teammates. i also suggest you have electrical storm because it can restore focus without hurting yourself like the baron who self pwns with his version of dark infusion.
I almost forgot to mention, do not save after you re spec because your re spec might not work so in case your re spec didn't work out, you can still try again without having to continually waste your money.
Now its your turn to help me, i'm stuck on Gregor and i can't seem to squash that bug because of his constant healing. I think i should try retronade which switches healing with damage but i haven't really yet. anyways, congrats and hurrayz