Add Blue Mages Already

[Seraphor]

I am sure we could come up with a fun and interesting lore reason, for why BLU spells are all instant cast or extremely short cast compared to other mages.

There's already some lore that could fit an original interpretation of a blue mage, and work for a tank.

Magitek.

Garleans magitek is basically the repurposing and replication the powers of primals and beastkin.
Think Ultima Weapon using the essences of Ifrit, Titan and Garuda but on a smaller scale.

Utilising a kind of magitek force field that absorbs damage and converts in into aether, can translate hits taken into magic.
Blue flavoured magic.

Could also explain it being a mage in heavy armour and not requiring cast times, because it's magitek and not incantations and whatnot.

[Rongway]

Magitek. [...]
Could also explain it being a mage in heavy armour and not requiring cast times, because it's magitek and not incantations and whatnot.

This is a reasonable possibility for how blue mage could be a heavy armor tank. We don't need another heavy armor tank right now, though; we need any kind of tank but a heavy armor tank. The people who want to play heavy armor tanks are already playing heavy armor tanks. We need a tank for the people who want to tank using a different tank type.