I don't have a problem with the planet advancing that much in several hundred years. They seemed pretty 1500s pretty early in the episode. What I have a problem with is that, after Jin said "We're not ready to join the rest of the galaxy yet", a few seconds after ships didn't emerge and say "Okay, we're ready!"
This may be one of those "barely legible screen canon" issues (which is to say, how much stock can be put in decision made by the art department), but the settlement at the beginning of the episode betrays that the state of civilization is more advanced than the script suggests. It's an alpine settlement that already has its own monumental architecture (the large hall). Not only does it suggest that they are not hunters-gatherers (they have permanent structures), but there exists extensive trade and agriculture elsewhere that is not being depicted. Such settlements become possible around 2500 years ago, becoming more prevalent about 1500 years ago. So the pace of development isn't being accelerated as much as the episode might otherwise portray. It's not the 12000 years of agricultural development or the 6000 years of urbanization.