x-Eveelution-x

Bartz was a mime and Onion Knight was really just a class. Main characters always have a distinct difference from other party members, Once you got into IV and later, every party member was unique (except in VII. Bunch of generic unlikeable character that I still wish would fall down a set of stairs on fire).
Cecil class changed and had unique abilities, along with many of his team mates
Bartz was a mime as I pointed out
Terra had Esper powers (although the Rages were still the best abilities in that one. Stray cat roflpwns j00)
Kneeling journey dressed in a cloak of shadows.
The hunting’s grim for the innocent eyes.
Communion’s prey is a cup of sorrows.
But faith is colours for the humbling cries.
What I'm saying is that a good number of the heroes could technically be whoever you wanted them to be, they didn't have a set class, the only thing that set them apart was their weapons and limit breaks.
Warrior of Light - He could be one of six job classes, just like the other three.
Firion - His stats could be upgraded in any way you felt like. The only thing that made him somewhat unique (but not really) was that he used swords, I don't recall if he could use others though.
Onion Knight - Any four of them could be any job class they wished.
Cecil - Starts as Dark Knight, becomes Paladin. FFIV is one of the only titles with set job classes. FFII kind of is.
Bartz - Just like Lenna, Galuf, Krile, and Faris, he could be any job you wanted him to be. Any of them could be a Mime, and none of them were forced to be.
Terra - She's her own job class, just like the rest of the class.
Cloud - He may have higher strength and stuff, but he could technically be a pathetic white mage if you wanted him to be.
Squall - Ditto to Cloud. He may have been the most powerful, but you could have made any of the other characters the tanks while he's the healing mage.
Zidane - His own class, like the rest of the cast.
Tidus - His own fighting style, and he's made to be his own class like the rest, but you could still technically take him elsewhere on the Sphere Grid.
Really the only thing that separated FFXII's job-less system from most of the rest of the series is the fact that the characters in FFXII don't have set weapons or armor, and all of their limit breaks do the same amount of damage. But the other games' casts were just as customizable.