You know how frustrated you get when there's people in DF that haven't done their job quests and don't have key abilities, or when you're doing level 31+ dungeons and people don't have their job stone equipped, or arrive otherwise gimped and do nothing but slow down or even prevent a successful run?
Imagine that, but with EVERY Blue Mage you see.
Unlike other classes, BLU learns skills from defeating enemies, which means going out of your way to fight certain mobs. The average DF idiot doesn't even bother learning a rotation with skills the game GIVES you, so what do you think the chances are of meeting a BLU who actually has the required skills?
BLU will be great for a little diversion from the game. A cool little side quest. A little adventure all of its own that guides you to getting the skills you need.
But letting this out into the open where any moron can foul up a roulette would be a grave mistake.