Yeah, it sounds like xp is only going to be rewarded through quest completion only, so you won't gain additional xp from the mobs you kill while on the quest. This on top of all of the reading a new player will have to do to get familiar with all the game systems is what will probably take a while. Once someone reaches level 10, they should be fairly comfortable with the game at that point, and should be able to breeze through quests pretty easily, which will increase the rate in which they level up.

I'll be playing Arcanist to start (as will probably most players that already have maxed out battle classes) so it'll be interested to see how slow (or fast) leveling will be in ARR compared to now.