I get this, but at the same time in those games characters tended to be less statically defined by a single job either. Which is probably why I like multiclassing here, just to make stuff a little more oddball (magic archers or gunmages, engineering geomancers, etc. etc.)... though as I've already complained repeatedly the system doesn't support stuff like that very well.
The problem as I tend to see it is that the system is engineered in such a way that it encourages playing a "base class" and then occasionally multi classing for a powerful ability here or there rather than creating any sort of split identity. So it ends up being less a way to help further define your character and more a way to powergame by making sure your red mage has mind over matter and ancient spells (etc.).