It is in many ways much like coaching a n00b, but a n00b that can do 10 hours of n00b work in 10 minutes (or, 2 minutes).

That's a significant difference. There are a lot of tasks that can be done by a n00b with some advice, especially when you can say "copy the pattern when I did this same basic thing here and here".

And there are a lot of things a n00b, or an LLM, can't do.

The study you reference was real, and I am not surprised — because accurately gauging the productivity win, or loss, obtained by using LLMs in real production coding workflows is also not junior stuff.