I agree with OP, it would be nice if there was a way they could release gating for alternate classes/jobs. They could do this by preventing how much currency can be _spent_ on a job instead of earned by a character.

i.e. You can only spend a maximum of 450 tomes per week on a Job; however, this can be carried over* to next week for the purposes of purchasing chest/pants/weapon. You can then continue to earn more tomes, which could be used to spend on an alternate job.

*for carried over, this can be done in two ways. Automatically earning 'spending credits' for any job once it hits 60, and have it automatically transfer if unspent. Alternatively, there could be a button to spend credits by purchasing credits for next week, or "transfer remaining credit balance to next week."