Why not an alt instead of moving jobs?

[Mhaeric]

It is far easier to just switch jobs on the fly on a single character, multiple jobs use the same gear so you don't have to farm the same stuff three times over, and you don't have to complete content multiple times. The MSQ alone is incredibly long. There's also an exp bonus to your other jobs if you have one job at max level.

There are reasons to want an alt rather than a second job, such as role playing or wanting to play through the msq or even extra storage space, but none of them are related to being easier to level a job. It is far more efficient to level all your jobs on a single character.