I DON'T think there's a problem with the speed of exp gain at all. The only problem is people who decide to level super fast and then are sad about it afterward.
I've been playing FFXIV for over a month and my highest level job is still currently 34. I took my time to explore Shposhae, toto-rak, and keep myself well-geared and wealthy even though I'm still comparatively low level. I did this by playing several jobs, especially DoL/DoH ones, at the same time as my "main" combat job. To all those people that want leveling to be slower, why don't you just play the way I did and then leveling WILL BE slower?
Anyway, there's many important reasons why leveling should stay "fast" like it is now:
1. So the slow trickle of newer players can catch up with the majority of players who have jobs at level 50.
2. So people who have a job at level 50 can get their other jobs to level 50 without too much re-grinding of the same content.
3. So everyone can enjoy the new mid-game and end-game content they're working really hard on right now.
4. To give players a well-paced sense of accomplishment and diminish the sense of grinding
5. To not alienate less superhardcore gamers.
Reason number two is especially important; this MMO is pretty unique in how it lets you, and very much encourages you, to level multiple jobs. People really need to take that into consideration when they ask for leveling to be "slower." Making things slower would make leveling up your 2nd, 3rd, 4th etc. job much more painful.