HUGE pacing issue around level 40

[Able]

I hate to be this way, but it just seems like you're complaining about grinding. If you dont have a big tolerance for grinding, then I'd strongly suggest unsubbing immediately. You can't rely solely on quests for XP in this game.

[Moomba33]

Back at launch you basically had to FATE grind to finish off the 40s.

Things are much better now. Do a daily low level roulette, guildhest roulette, go after weekly Challenge Log goals (unlock the Challenge Log from a quest in Limsa if you haven't already), do FATES and Leves while you're waiting in queue for dungeons.
Quests alone are not enough for the higher levels but there are plenty of options if you look around.

If you find leveling too grindy at this point even with all of these options you probably won't enjoy the end of the 2.0 story. The main scenario jumps from level 46 to 49 at one point.

[seekified]

Back at launch you basically had to FATE grind to finish off the 40s.

This. The current state of things is actually a vast improvement, because there's so much to do that gives you extra chunks of exp. I basically fated my way from 41 to 50 in one day in Northern Thanalan on my first go (and then proceeded to avoid that area for a year), but now with challenge logs and roulettes it's much easier.

The whole story quest jumping from 46 to 49 thing is probably to encourage players to do Aurum Vale a few times. That place gives out insane exp if you kill everything, despite its bad rep, actually has some interesting fights.