And Jecht would've made a better choice than Shuyin, definitely. For one thing, we don't need two characters who fight the same way. Also, after 1000 years as a phantasm, Shuyin had sort of lost most of the personality he may originally had, and had replaced it all with simple hatred for everything, while Jecht, though he had become a psychotic killing machine, still had a lot of his feelings left.
Simple psychotic killing machine? Tha tonly describes 95% of FF's villains...and they don't have actual reasons for it like Shuyin does. They just want to take over and/or destroy the world
(("OF COURSE!"))

And I dunno. I guess you can just forget X's ending where Tidus and Jecht share a tearful reunion and then Tidus giving his father a happy friendly handslap as he leaves for the Farplane. just forget that and say they don't like each other and have them fight. Makes sense.....