Even most boss fates can be done solo but it helps to have potions. Ever since PotD was released, it has been cheap to carry around whole stacks of max-potion HQ and guzzle them as quickly as the cooldown timer allows to sustain oneself through long solo battles. I have 10 jobs at Lv70 so far and I basically just cruise around looking for fates that have bonus exp while weaving in dungeons and duty roulette.