Im a sage healer, and that is exactly my biggest problem in that fight. It is so much easier to heal if people just spread out a bit (staying in range for the AoE heal) and stand still. There is no need to run around as headless chickens.
As long as people stands still and makes sure to interrupt his headshot ability, the fight is actually not that bad.
The interrupt didn't work for me this morning. I was standing right on top of him and my interrupt key was greyed out.
Of course this resulted in a wipe and the healer promptly QQing in general what an amazing healer he is but just couldn't keep us alive because we suck...