Citadel de morts help

I’m looking for insight or help on the final boss for the citadel does morts map. I have absolutely no problem getting to the boss fight, but I just can’t seem to make it past half health without dying.

I go in with an xm4 PAP 3 max rarity, all perks, mutant injection.

I have no idea why I can’t get past the final fight. Any help is much appreciated.