Khimari is the only character that feels incomplete compared to the other characters. It is obvious that he was intended to fill the role of Blue Mage / Dragoon, with using a spear, having the lancet ability and having a blue color scheme.(Yuna wears white and is a white mage, Lulu wears black and is a black mage) He was just lost somewhere in the process, and never really picked up.

I think that the original intent was to have blue magic be similar to summoning, in that it would be an extra command available only to Khimari, so to make up for it he would have a smaller section of the sphere grid. But that idea was dropped, and the sphere grid map stuck.

Also a response to the thought of Khimari as a hulking character, he is a very small Ronso, so by their standards it's not that surprising to see Khimari as a mage. But any way you look at it, he is very easy to pass over.