We used to have this:

Gladiator+Conjurer = Paladin
Marauder+Gladiator = Warrior
Pugilist+Lancer = Monk
Lancer+Marauder = Dragoon
Archer+Pugilist = Bard
Conjurer+Arcanist = White Mage
Thaumaturge+Arcanist = Black Mage
Arcanist+Thaumaturge = Summoner
Arcanist+Conjurer = Scholar
Rogue+Pugilist = Ninja

It was a tedious chore to level an unrelated class to unlock the job you actually wanted. It was good in that it got you to try other classes, but often they were just not what you were interested in. It was enough to put people off the game or come across complicated or confusing.

Over time, SE removed a lot of pointless or tedious things like that, and doesn't even make classes anymore.