Instead of focusing on "Job types" focus on "battle types." Maria is meant to be a mage, yes. But that leaves her other stats lagging behind. Firion can be a good warrior, but he also has a capacity for magic. Again, it's up to you, but the team i always used was:
Firion, All weapons and Black Magic
Maria, Staves, bows, knives and white magic
Guy, Axes, Bare hands and a little bit of white magic, only to be used in emergencies
Leon, Obvious
And don't forget about the shields trick for mastering weapons. Just master the magic FIRST.