That fight wasn't the most difficult fight in the MSQ line- not by far. I beat it on my first try as a BLM. By then, you'd already had plenty of practice fighting him (even by using Thancred) and there wasn't really anything new. I barely remembered the fight and had to look it up to remember what the fight entailed. Obviously the fight wasn't memorable.

So yeah, either something bugged and screwed up, or you missed something. That's all. You get over it and go again. That happens sometimes in games. You move on.