How to beat "The Reason Roaille" as a white mage

[Arcanon]

Honestly it feel like this game punishes you for being a healer. if you try to do anything on your own, you will immediately get slapped in the face told to go home. But anyway I've hit a quest wall with this one and i can't seem to get past it. I start the mission kill their healer first and try to pick off the rest of the adds while giving heals to the main guy when he needs it but when they get reinforcements and I kill their healer again, by that time the rest of my team is wiped out besides me and the main guy until either me or him is killed and them duty failed. I have tried this multiple time with and without cleric stance and neither works. My item lvl is 107. I just want to get this story crap over with so I can get to the content I paid for. okay proceed to tell me how much i suck.