I think the conclusions miss the mark slightly and focus on a symptom of good bosses: they care about tasks from a state of understanding what is required to do them well, they have empathy for the challenges, and respect for the talent in completing them. Obviously the easiest way to get to this perspective is to experience it first-hand, hence the correlation between those who could do the job and being good managers of the job, but I don't see this as a requirement, just a common path.
I also don't see this a refutation that we shouldn't hire good engineers into management, rather we shouldn't do this blindly and as the single criteria. My best managers were all top quartile engineers but probably not top 5-10%, because they also cared about the non-technical requirements that a good manager needs to cover, and this inevitable consumes focus, effort and time that your best engineers don't want to allocate.
I'm a relatively new engineering manager (~3 years) and wrote about the traits of a good development manager from my perspective here:
https://www.codeleadmanage.com/articles/20200204-four_qualit...