I didn't find the Oerba boss to be that challenging so it is hard to say what to tell you to do differently. In fact, I would probably say that aside from not being maxed out in the roles, your characters and monsters are probably built better than the ones I used for the fight. So it should be very easy for you to complete, just time consuming.

I went in with Golden Chocobo, Flanitor and the Sentinel flan, I forget its name. Flanitor and Golden were maxed on leveling but did not really much in the way of infusion. They were pretty much as I received them, same with the Sentinel, I just hadn't finished leveling him. I was using ATB +30% on Serah and I think Odin's weapon on Noel along with the best version of the Kaiser Knuckles. Serah was just +33% physical resistance.

Paradigms were COM x3, RAV x2/COM, SABx2/MED, SYNx2/SEN, MEDx3, SENx3. When I fought it I focused on killing the minions it spawned first before continuing back on the boss again. I made sure to get the stagger to 999 before going all Commando. Take advantage of the Paradigm switch bonus every 2 turns. Keep your buffs up and what debuffs you can on. I think the Deshell and Deprotect had trouble sticking, so if you want once it is stagger debuff. While enemies are staggered they are easier to debuff. Then after that just unload Ravager until ready for Commando.