Amusingly Vaan is much more interesting when he shows up in any Ivalice Alliance Game that's not FFXII. In Revenant Wings and FF Tactics A2 he's a lot more of a fun character, and in the former much more of a protagonist. Part of the problem is that the story went through extensive rewrites, with Basch, Balthier, and Ashe all having been the protagonist at various points. Initially Vaan was going to be revealed as the prince you played in the intro (hence their similar appearances) but this got cut leaving him just kind of ...there.