I always find it odd when people complain about leveling gaps, because I'm always overleveled. I've spent the vast majority of my time in this game being scaled down.
If you're having trouble, you need to explore other aspects of the game. I'm doing basically everything, exploring (including getting full clears), story quests (HUGE rewards for these), crafting, events, hearts, going on runs to farm materials ("farming" in this game is more like running around for 15 minutes than the all-day activity in other MMOs), going out of my way to take out passive mobs that give massive bonus XP for being untouched for so long, etc. You don't even have to do all of these; like I said, by trying out everything, I'm actually overleveled constantly. Just do something besides running from heart to heart. And you can do all of this in any area you'd like; although you'll be more productive in something level appropriate, low level content is less complex and goes down pretty quickly. Getting 400 XP for a quest that takes no time at all as it gets zerged in a starting area full of new players is actually fairly productive even though the numbers that flash are smaller.
When you hit level gaps, that is the design of the game telling you to try something else. I have a feeling that, like with most other MMOs, the bitching over that choice will lead to it being patched out, but I hope not. Encouraging players to participate in many activities instead of tunnel vision quest grinding can only be a good thing for the quality of the community.
