How is the level grind when compared to FFXI and/or WoW?
There are 5 major sources of exp in the game:
FATES (world event quests that pop up a lot)
Your Hunting log (kill 3 of x mob for an exp bonus, big bonus for completing 10)
Levequests (repeatable Fate-esque quest events specific to you that you choose)
Dungeons/Guildheists (the latter being party-based levequests that probably aren't really worth it except as a teaching mechanism)
Each city territory has quest hubs through cap (or up until close to it, at least). Each city is probably good for getting one battle class up to 50 once combined with FATES, leves, periodic dungeons, and the hunting log.
There is a main story line, and that quest series is essentially worth another city. Doing that, plus the hunting log, FATES, levequests, and dungeons is essentially how I hit 30, without touching much of the other quests on my Cnj.
So that is 4 classes to cap without grinding.
After that, it's just the Fate events, repeatable leve quests, hunting log, and dungeons.
I should note that Fate parties (go from Fate to Fate in a group as they pop up in a zone) are easily the fastest way to level in game right now, and they're super active (you're generally always killing stuff or on the move).
So it's not so bad. Might be sort of boring if you intend to take EVERY class up, but just judging by how fast I hit 15 on my Arcanist versus my Cnj, the exp buff for the class level difference is DEFINITELY noticeable.
I'm guessing the game is primarily structured so that getting a class to level 36 or so (when you'd get the last of the cross-class abilities, more or less, from that class) is meant to be relatively easy, but the last 15 or so levels are longer to get through.