A number of FF titles had numerous jobs as a core mechanic. Adding more jobs is essentially adding to the job/armory system. The cause of the complaints about jobs within the same role feeling so similar is less so much the job design and more caused by the way they've dumbed the game down when compared to other FF titles. Elemental resistances pretty much dont exist now. Damage type resistances also pretty much dont exist in this game. Gear selection dumbed down to being nothing more than just get bigger number in this substat. I mean... we're killing fire elementals with fire damage, easily stabbing flan and slime type monsters to death with knives, spears, and arrows, we could steal HP from undead enemies, the list goes on for stuff that wouldnt really work well if at all in just about any other FF title.

Then there was caving to all the thread of people saying "X job has this. I want it too".

As far as jobs for the next expansion. IMO I feel like 1 needs to be a healer. Personally I think I would go the route of making 1 healer, 1 tank, and then 2 new DPS. The 2 new DPS being 1 job that would share medium armor with DRG and another that shared with NIN as those 2 DPS jobs pretty much have armor sets all to themselves while everyone else has to share...