Have you tried Lure Magic and Reflect instead? Steiner and Agrias can self heal with Drain Strike. A Runic RW can mitigate as well, though it'll do less damage because Golbez always casts the same element that he's weak to, so reflecting those will up your DPS a noticeable amount.
Got him down to about 25% hp left. He was casting too many aoe spells. Binding cold paralyzed several people as well.
Im running out of dps towards the end as well.
Need more ability slots. Question, does shellga bypass my reflect from carbuncle?