This is working off of a couple of earlier ideas, but figured I'd just start a new topic to consolidate things. Frankly, the only distinction between Classes and Jobs right now, is that Classes are basically just worse versions of Jobs, in virtually every scenario. So, I'd like to propose a couple of changes.
1. Ditch the term "Class" entirely
No more of this "Which is a Class and which is a Job?" nonsense. What we need, moving forward, is a consistent terminology to work with. Break them down as "Base Jobs" and "Advanced Jobs" if you must, but call ALL of them "Jobs".
2. Soul Crystals, *NOT* Weapon, should dictate your Job
From the moment your create a character, you'll have a Soul Crystal. Even the currently-existing "Classes" will have Crystals. The reason why is because...
3. Allow different Jobs to wield more weapon-types
Right now, Gladiators and Paladins both use One-handed Sword. After this change, however, Gladiators could now be free to wield one-handed Spears (which Dragoons could now dual-wield), while Paladins might gain access to Two-handed Swords (which Warriors could also use, as well as Dark Knights later one).
4. Give every Job its own niche
When I think "Gladiator", I mentally envision a Spartan warrior, or a Roman pit-fighter in the Colosseum. Instead of simply unlocking the Paladin and never looking back, the Gladiator would them totally deviate, becoming more focused on mobility and dealing damage with their shields. Similarly, the upcoming Rogue (we all know he's really a Thief) would remain unique, focusing on gadgetry and cheap tricks, while the Ninja would explore their magical Ninpo.
5. Give each Job its own Relic/Artifact Armor and Weapon
If you really want to seal the deal, giving each Job its own distinct "look" is the key. Gladiators could get a Greco-Roman set of armor, leaving their chest and part of their legs exposed, and Archers might get a hood and cloak to help camouflage them (high-level variants could maybe even change color, depending on the environment?). Even if they're statistically identical, it would really make them *feel* different.