So I ran the latest dungeon a few times. I can now agree that Flamethrower will lower your DPS even if you do the full duration. Better to just do other AoE attacks. Do yourself a favor and delete it off your hotbar.

Also I noticed I do super low DPS in comparison to just about any other class. Like I'll be in 2nd place in terms of DPS...but the one in 1st will be leagues ahead of me. My Ilvl is good and I would say I'm fairly competent in the role. But yeah even with me trying my hardest I couldn't get near 1st place in terms of DPS.