I thought the light boss was way harder.
The dark one I just medium special'ied to death but the lightie...man..he kicked some serious butt and when he did that I started laughing hysterically and wasn't able to defend myself anymore.
I thought Desann was a wimp. I ran in and hacked at him a few times with red stance and he was dead. Game over in like 5 seconds.
I guess luck has much to do with beating end-bosses.