Since the launch of 2.0 the best way to level had always been FATEs, or dungeons which would be a bit slower, but a lot less boring. In addition to your first 50 kinda being handed to you with all of the quest rewards. Still, leveling another class wasn't too bad.

Now in 3.0 I'm already worried. My first 60 is obviously a breeze with all of these quests, but what happens when I want to level up another? So far the only things I see giving reasonable amounts of xp are duty roulettes, but that can only be done so much in a day. After that what is there to grind that gives good xp? FATEs are absolutely horrible now and so are dungeons.

Am I completely missing something obvious or is there no real non gated way of grinding another class up?