I don't really have any idea about class/job design, but I would say if there is only job or only class (so no upgrade of any kind), I would agree, but the guilds would have to be reimagined. Instead of having specific guilds, I would just have the adventurer guild be the sole trainer for multiple classes/jobs. That way you can add as many new class/job with new expansions and each of them can be the starter class/job instead of having to level a different class/job first.