Dungeons are getting an XP boost in about 2-3 weeks so you will be able to do those. They are also boosting the XP reward from guildleves as well as adding more quests (including repeatable ones).

So essentially once that patch hits you will have multiple viable means of leveling up besides FATEs.

And don't forget you get a 50% xp boost just for having a class higher level than your current one.