!!!!WARNING MAJOR XIII SPOILERS!!!!
(SPOILER)I know that but I feel the abrupt "betrayal plot twist" combined with the whole "you inspired me to actually be the guy you thought I was" was poorly implemented and the whole thing sorta felt like the writer was trying to tie up that loose end and basically pulled a BS story twist to quickly sweep him under the rug. A few good chapters were being used to build him up for great things and I feel he never lived up to them and was poorly utilized in the end. He had potential to bring a lot of depth in the story and I felt he was used for merely a cheap emotional ploy on the player. They could have at least built up his betrayal and him finally turning against his Focus but it all comes crashing down at once in Chapter 10. At least he was a fun boss fight.
Its my same problem with VI's Cid, beyond the whole scene where he can die, he really isn't that important of a figure in the story despite all the background info and basic elements of the character saying he should be a greater figure in the story cause what he's been doing in the background has had a profound effect on the plot despite the plot never directly referencing or delving into it. He could have easily been a major player in the plot but basically got shafted like many of VI's NPCs.