It could have work.
If solo content was more interesting and engaging.
But it's not.
Leveling with trash mob isn't even something you do with other classes, yet, that's something common on MMO, but not in FFXIV.

It looks like a sandbox job. It looks fun time to time, then you forget it.
Disappointed of course.

They could have make blue mage work on every content by putting some restriction on some monster skills. Overworld, you can use everything, on its dedicated content as well, not in raid and all.
So it could have had a "rotation" on more streamline content.

And the excuse "do you have each skill for this content", see the restriction above.
Besides, you don't let a blue mage queue on duty finder with no skill. Since we know he can have 49... well, just be sure you can't queue until you've learned them all so they don't come naked lol.