I'm wondering if there's really any other way to look at it.

Penelo is pretty unanamously considered the #6 is this game, and I think you would be hard pressed to rank Fran ahead of any of the other 4 in terms of either relevance or usefulness.

Ashe is the strongest Mage, and it'd be really really difficult to say that any of the other guys are more important.

Balthier is more relevant and charasmatic than either of the other 2 guys, which just leaves kind of a debate on whether you put Vaan ahead or behind Basch