I believe Yoshida has stated several times that he is not eager to implement Blue Mage in this game because they are not MMORPG friendly or something. Perhaps someone could pull up the quote.
The same thing can be said of Red Mage though in that this MMO in particular is heavily designed around the specialisation of roles in a party. True Red Mages lack specialisation and nudging the class to favour any single role above others will piss off at least half the RDM fanboy club - because those people don't understand compromise.
My vote is for Chemist as a Healer or Corsair/Fusilier as DPS.