Job changing has been a running possibility in the FF series, and although I agree that some characters (like Tifa) seems to be more appropriate for some job (like monk) there is no definite obligation for most of the FF as stated before.
Having to use only one avatar and being able to do everything with it it THE thing that got me into playing FFXI and XIV, creating a much deeper attachment to said avatar. I would not trade this for the world.
Even if I can play any class correctly, my LS mates now me as a monk player, and for most of my LS mate we all have one or two job that we main and at which we are at our best (with the possibilities, if we need of feel like a change to play something else entirely), this did not prevent us from clearing all of 1.0 content, relic and white earrings included.
