Blue Mage balance can be mitigated by making anything more potent than Flare/Holy a "slotted" limit break effect. Limit break comes in 3 levels, so it allows powers that are normally restricted. I've heard of a limit break doing over 27,000 damage. By hiding high level powers in dungeons with i75-90+ gear requirements, you can also keep blue mage power scales comparable to other classes.
Still, while Blue Mage is obviously DPS default, it would be interesting to think of them in terms of a Tank.