> It is plain to see that the developers who prompted an LLM to generate this library will not have the same familiarity with the resulting code that they would have had they written it directly

I think that's a bit too simplified. Yes, a person just blindly accepting whatever the LLM generates from their unclear prompts probably won't have much understanding or familiarity with it.

But that's not how I personally use LLMs, and I'm sure a lot of others too. Instead, I'm the designer/architect, with a strict control of exactly what I want. I may not actually have written the lines, but all the interfaces/APIs are human designed, the overall design/architecture is human designed, and since I designed it, I know enough to say I'd be familiar with it.

And if I come back to the project in 1-2 years, even if there is no document, it's trivial to spend 10-20 minutes together with an LLM to understand the codebase from every angle, just ask pointed questions, and you can rebuild your mental image quickly.

TLDR: Not everyone is a using LLMs for "vibe-coding" (blind-coding), but as an assistant sitting next to you. So my guess is that the ones who know what you need to know in order to effectively build software, will be a lot more productive. The ones who don't know that (yet?), will drown in spaghetti faster than before.