Yeah, Vaan is definitely better as a supporting character than the protagonist. In his own right, he's a fine character, but then the game has to try to assert his relevance.

I've said this already, but I do think Final Fantasy XII is a [very] flawed masterpiece. It suffers from borrrowing Star Wars plot elements, but it also does really well in its villains and supporting cast (I love Al Cid and Ondore), and the world itself is wonderful.