So I haven't played the game too much in the past 9 months or so and when I played peopled leveled by doing Fates.
I don't see Fate parties anymore and have been doing leve quests but there are 2 problems with that. One leve quets are finite and you need to have access to them, also they can only be done solo and this is an mmo? (I guess one includes 2 things) Two there are sometimes gaps between effective leve's and level. For example level 20 leve but no level 25 leves, no more until 30, you can do grand company ones but they don't give as many and they don't seem to give as much exp.
So what other than leve quests do for leveling? I do also que for dungeons but if you are playing dps it can take a very long time to get into one.