I mean, this horse has been beaten, rez and beaten again, but it's totally possible to have BLU working like a "spell collection minigame" AND a proper PVE caster.
Just have the job quests revolving around collecting a specific set of spells that are designed to work in PVE group content. Heck, make the BLU spellbook have a separate section for them.
Blue mage could fill as a support-type caster, like Red Mage, but with different niches.
