FFVII and VIII characters where clean slates, they would've been virtually the same character if Limits were not unique abilities in those games. In IX each character was unique due to their specific skills so Unique abilities weren't necessary (although I agree with Zidane getting new Trance abilities merely because it would've sucked so much had his Trance been better stealing or his crappy Thief techniques).

Also I felt that Trance was built up early on, specifically for it's use with Kuja later on, I fail to see how they said "Meh, screw it" when so much of disk 3 and 4 was built on the idea of Kuja needing to absorb hateful souls to attain his own trance.