A single expert in a team of juniors can do so much more. Because it can delegate the junior work to the juniors while doing only expert work.

This part is definitely true but I think it misses the point. A single expert can be a force multiplier, or they can be overbearing dead weight. There is the possibility a technical expert wants to micromanage and see every step as it is done (thus holding up work that can be done while the expert is elsewhere).

I conjecture that those skills and attributes that separate the two experts we’ve described is what “good leadership” consists of.

I would never trust a leader who has no technical skills, but neither would I trust a leader who has only technical skills.