3 jobs would have been better, but that's OK. Let's settle for less when we could have had more!
The ONLY identity for blue mage that's been consistent is that it learns abilities from monsters, then uses them on their own. They have never had a full carnival sidestory, and they've never been excluded from participating in the game itself. You can bring Quistis or Quina or Kimarhi with you the whole game.blue mage is just an extra thing devs did because so many people kept asking for it, and from the looks of things its going to be pretty damn close to how an FF Blue Mage should work.
It would likely take less work to do that than to do the Carnivale and balancing that. The difference is BLU in relevant content is a better long-term option than being relegated to content that'll last, at most, about 6 months (and only because people will be bored as hell with nothing new coming after 4.5.)If they were to make Blue Mage a full on job it would definitely have to lose a lot of its essence as a blue mage to stay balanced with the other jobs and work with the newest content.