The biggest issue that I ever had was that his shield comes back stupid fast. Hitting him with something that has DOT keeps it from coming back. Thorn is a good one. Or incendiary grenades on hunter. Or use the grenade burn perk with sunsinger. So drop shield with arc weapon, do damage, apply burn, reload, do damage before shield comes back. If you have a couple people and everyone focuses fire, shouldn't even need to burn because he should be getting hit at all times. So his shield should not ever come back.