Idk, I did ACN 0-49 so far almost completely on quests, only running most dungeons once (not just the main story ones, but all optional ones as well). There's always side quests in the areas the main story takes u to, plus I did all Guildhests and my class/job quests a long the way. I made it a habit of completing every quest in the area before moving on, which actually delayed my main scenario progress significantly. Then of course i completed the Hunting Log, which the main story also pretty much takes you to areas where the mobs for that are if you pay attention. But there were only a couple times I had to grind exp, both in Coerthas, and I did that on leves.

I think SE did a really good job with the quest progression. Every time you get to a new area there's lots of other quests you can do before moving on, most of which are from the same NPC or only open up at other NPCs after you have done certain other quests in the area.

This will get one of your classes to 50 quite easily, and I don't think it should be possible to quest every class to max lvl. It's just too fast and easy.