Xehanort is certainly a skilled fighter, but he’s not ready to deal with someone like Vegeta. Vegeta is the Prince of All Saiyans and as such his abilities are considerably greater than that of Xehanort’s. His Big Bang Attack can wipe out a planet in an instant and with his speed Vegeta can dodge all of Xehanort’s counters with ease. It’s a one sided match from start to finish. Vegeta wins.