The fastest it still FATES...so this would be the best case for you:
1. FATES grind while waiting for your dungeon que to keep the XP rolling in.
2. This way you are learning the job in the dungeon and how to play it and not just how to get Gold credit of the FATE.
3. These jobs are okay to start out at 30 because they are very similar to other jobs in how they work.
4. I just looked at my Astro's abilities and set up my bar in a few minutes and did Haukke Manor with no issues while dpsing almost the entire fight.
5. If you know who to play the game it is really easy to pick up the new jobs with just a little practice in dungeons.
6. YOu also have to make use of your CHALLENGE LOG that gives great XP if you use ALL the options it provided each week.