Was able to 3 box this mission with 75 Ranger (14K / 2600AC buffed and with shield), 75 Cleric, 75 Shaman. The key is positioning.
Well straight off, ranger tank was shaky, as the big hits were wicked scary. But after 3 attemps at different tank locations, found the gem.
The key is location. On the right side of the ramp, on ground level, where the ramp creates a corner with the wall is perfect, no mobs repop there, and out of agro range of all.
Had cleric and shaman stand in the corner facing out, with Ranger a few inches in front to tank the boss. Had to move out a bit, as ranger reach was a wee bit less than the Guardian. As long as the Guardian was facing the corner, his AE did not disrupt any spells being cast.....Chain CH, and shaman best HoT ftw.
The first 60% is very simple....doesn't hit too hard, and used that time to mostly just gain agro. The last 40% and specifically the last 20% were rough. The AE is a huge pain, but with some well timed Thundering Blade procs, and Weapon Shield at 15%, following a full out shaman burn starting at 30%we prevailed......Started getting hit for 3500+ at 1% and thought I was done for, then 1 tick later, CH landed and the Guardian took the dirt nap.
So you don't really need that big a group for this anymore, just a little patience.