This slide from https://www.youtube.com/watch?v=w3EZpcTZ4ZA describes the 10× developer pretty well:
“1/10th of the time, and achieving in 1 week what a team of devs used to deliver in 1 month”
One week instead of one month is not 1/10th of the time. Even considering dev vs. team, it’s: Overestimating the value.
Later in the video, he explains that about 60% of the code is technical debt that he needs to fix now.
So what would have worked after a month looked good after a week but didn’t work.