Well XI didn't have a multi-layered Class -> Job system so the conventions used there may not hold true for XIV. There's really no precedent for this kind of a system for FF. There have been Jobs -> Other/Advanced Jobs but they're generally completely separate.

Considering classes and jobs are linked more intimately, it's hard to tell how it's going to work out. When a class progresses in level, it indirectly increases the power of the job (stat wise at least). Job progression is kept separate from the class though as it is done through a series of quests/missions.

Considering this, there would need to be as many job sets are there are class sets to keep up. Otherwise given enough time the class armor will overcome the job armor stat wise. However after a certain point, I can't really see using the classes. From what I've seen so far with the skill lists, it seems like you get the job skills on top of whatever class skills the job comes from. The WS combos for jobs that branch off of classes lead me to this conclusion.