They actually already have a move in the game that splits damage evenly with Blue Mage 1000 needles. So it wouldn't be impossible.

Despair feels like a mostly useless skill only for ending Astral phase. I don't really like using it at all. Visually unimpressive and barely stronger then a Fire 4. Disappointing attack over the 6 F4's I throw out.

A lot of button bloat could easily be solved by implementing the combo system they use in PvP where you use one attack and it changes into the next attack in the 123 combo. Makes sense and easy to do.

A good point is synced content locking you out of your toolkit feels awful. It's why Blue Mage is so damn good. Regardless of the content you do you always have your full kit at the ready. If I have to do synced content I always want to run as my BLU.

BLM feels bad when you only have Blizzard 1 or Fire 1 compared to Blue Mage's everything.