People are weird. It's just better to create a new job.

As blue mage can do everything not just red dps. You can solo any dungeon as blue mage is eligible for with basic instinct because it allows all the role buffs without the downsides. Revenge Blast is sickeningly good that encourages a raid of blue mages to stay at lowest HP possible, that's good stuff after getting smacked by a lot of damage. There are many different play styles encouraged and that's what made doing the sync'd raids exciting.

There are no traps. You can also get away with 1 blue mage tank in most of the non-echo sync'd raids because how stupidly good Mighty Guard and Diamondback is. Frog leg a voke and take a buster, tank takes it back. That kind of flexibly is awesome.