Please do not lock Jobs to the Weapon Class that unlocks them.

[Cairdeas]

Your weapon is locked to your class.
Your class (may be) locked to your job.
Your job is locked to a set of skills.
Your set of skills is locked to your role.

Why do you keep using Class and Weapon as if they are two different things?

Anyway if thats how you want it thats fine.

How I'd prefer it is

You Equip your weapon and are identified as being a user of that weapon.

When you level your weapon skill up to the appropriate rank you learn to specialize in a specialized role.

This role is given a name and called your Job (Job and Role are synonyms after all.)

Once you master this Role/Job you are now able to equip any weapon you want and perform the same role as long as your skill with said new weapon is on part with the requirements of the Role.