> In reality, I only need a few thousand lines of effective code out of it. If I were to do it all on my own, it would likely take two to three times longer—perhaps with better or worse quality.

Have you tried doing it on your own as comparison?

Any lessons why that might be true?

Are you missing some design/brainstorming stage that you are doing now by iterating through junk code and which might not be necessary?

You might be right now, but you gain experience that you otherwise lose by delegating to the LLM. With experience the reverse might be true.