Vayne never went nuts. He never went insane really. He wasn't some crap psycho in the end like Kefka. Sure, he got power hungry, but he just wanted, to be a Dynast King, free people from Occurrian control. His methods unorthodox yes, but he knew when the end was coming, and admitted that he had pretty much brought about the end of his own life - very much like a human being. These other villains didn't seem to recognise failure, they never recognised that their ignorance blinded them. Vayne was different. He knew when things were all over.

The end battle probably featured Rozzarrian forces - the resistance vs the Empire was a mix of people. Just Rozarria vs the Empire alone would have made the Resistance seem pretty pointless in the game.