I had a harder time with this bounty than with the Mowrghek Îen fight (to follow another posters no-spoiler-method) on PotD. At the same level (16) and basically the same gear quality.
What ended up working for me was doing some really high maintenance on my Cipher to keep him alive so he could continuously AOE CC the mobs since they do tend to cluster up and then focus fire the druids.
Also used elemental resistance pots on everyone.
Second hardest encounter in the game for me, following Adra Dragon PotD. I guess my party comp just didn't mesh well with the encounter. (Fighterx2, ranged Cipher, Rogue, Paladin, ranged Priest).
So satisfying to beat though when it's been such a brick wall.