I was under the impression that Zidane had been on Gaia for a long while before Kuja went crazy with his power. I thought that Zidane was on Gaia to take Kuja's place when Kuja's life ran out. But I do agree with you on the battle, Kuja would win because he can trance. This is probably why he was so fascinated with being able to trance, because if he could he would become more powerful than Garland.
