I've never had a problem with this, I just try to keep up Regen on him but I've never even had him get close to dying. Maybe it's just bad tanks? Also PS4 controls are no excuse for anything, I hated them at first but now I love them. There's so many ways to customize them just have to get it the best way for you. I don't have it open now so going by memory, but the way I have mine set is L2 plus R1 cycles targets you are facing to right right, and R2 plus L1 cycles to the left. That's the main way I select enemy targets. Can also hold down L1 and press up and down on the d-pad to select enemies in the enemy list, moving up and down from whatever one you are on currently. Then I have it so that up and down on the d-pad cycles the party which is my main way of healing. If I'm targeting the boss and attacking it, I just hit up or down to select the target, and then cast on them, or hit X to select them and then cast. I then have it set so that left and right on the d-pad cycles the party/alliance/npc as this is the main way I'd target him in this battle, or target other players if I need to heal them like in the solo quests.
