As others have said:

1. Roulettes
2. Beast Tribes
3. Spam highest level dungeon
4. Repeat

BT's in particular are great for jobs you don't want anything to do with in dungeon/battle content, so I'd recommend using those to level a 2nd job on the side that you hate and use your roulettes/dungeon spam for something you care about.

If you get tired of the grind, book skips are available for purchase in Mogstation.