Side quests should give enough exp to level a job to max.

[GrizzlyTank]

MSQ gets you 90% of the way there on your main job.
Side quest + Fates + roulettes doesn't it for your alt jobs?
They have to give people a reason to do all content 999999 times.
Also, WT is like 1/2 a level

Side quests are finite. So having them carry at least one job to max wouldn't have hurt.

Especially since their rewards outside of minor world building have been so bad that I've been more often than not drained than happy after doing those.