+1 on this, cleared today on a +12. What worked for us.
We noticed if everyone split up and tried to "manage" explosives that all of the hexers just spammed explosives. So we tried to all stack on one hexer and not put a single point of dmg into the other hexers. This worked!
The other hexers would only spawn like 1 orb every minute or so and the guardian and witch doc also would spawn alot, however we were able to clear them.
That being said, I think this is vastly overtuned and needs to be looked at. There is no feasible way to clear in time with the last boss having to single target each hexer down with zero cleave/off dotting.