What if instead of "levels" for jobs why not something like FF tactics where you earn ability points while you have said job active in which you can choose how you wish to customize your job. At the same time, the guild marks used for said class could be used to obtain additional abilities for the job, rather then make it purely leveled based. Perhaps then each person's "job" could be unique where one paladin might have more curative properties while another person's paladin might be more defensive based.