While I leveled up Ninja, I did only max. 10 leves in total and dungeons only the highest I could enter + daily roulette and not more.
If you mix in Hunting Log, Guildhest, Leves (to get cheap equip) and do FATEs only if you only need 1-2 FATEs for the Challenge Log, then you don't need to spam FATEs or Dungeons.