I've heard the number seven before. I did one stint as a technical manager - not my thing, but it was necessary for a short time. I only had 4-5 direct reports, which was ok, because I was busy bailing out a project from a difficult situation. Had I stayed on, I would have had spare capacity.

The problem is that big companies promote people, and promotion past a certain point always means management. Which is stupid. Some of us dislike managing. Others simply cannot be decent managers, even if they were great at tech work. So you end up with a pile of middle managers who are either bad at their jobs, or who have been sidelined and would never be missed.

Targeting the number 7 would dramatically slim down a lot of organizations, and likely improve their productivity.

It is not about the number. Work-product can only be inspected if the inspector knows more than the author. The myth of management as a distinct and self-sufficient skill has created an environment in which the inspection of work-product is ineffective and that, in turn, has reduced all aspects of work to performance.

The 20 hours claim for admin tasks seems baseless with no real data behind it. Without any evidence or examples, it’s hard to take it seriously