I just defeated (SPOILER)Shemhazai. It was easy, I literally hacked and slashed the majority of my way through. I had Fran cast Bubble and Decoy on Balthier. Had gambits set up for healing, used the occaisonal Echo Herb/Vox and disabled black magic gambits since she changes her weakness and absrobs all else. I was surprised how easy it was. I mean after all, I did not even have to use a Mist Chain or anything. Though I did cast Dispel at the beginning to get rid of any magic she might have had.

I find that as I go along the bosses are getting easier, though it might have been due to being underleveled early on in the game.