This is the first Stack Exchange offering I've committed to since its start and I've noticed it had a large amount of content initially, counting over 27 questions per day, but by taking a look in the respective Area 51 Page, we (as of now) have 6 questions per day. Is this a drawback or is it typical to every new proposal in public beta?
This is normal.
First, check out the list of Stack Exchange sites, sorted by "questions per day". Scroll down to Mythology.
We're near the middle of the pack in all of Stack Exchange. In fact, we're in the top half of beta sites, in terms of activity. And there are six graduated sites with fewer questions per day than us, and a seventh one we are tied with. So, to reassure everyone, this is fine.
From personal experience (i.e. two other private betas, and a third beta in which I just missed private beta; not a lot, but a decent amount), I can say that this is normal. There's always an explosion of questions/answers/activity during private beta, as there should be. It's nearly impossible to sustain that pace. Why? We've built up questions prior to launch, and the start of private beta was akin to the burst of a dam. Now, our reserve is gone; we may never get to that level again - which is okay.
Gilles wrote up a comforting answer on Meta Stack Exchange, which essentially says the same thing. Here's the "typical growth pattern" graph he made: