So the heuristic works only so far as you can make a good enough guess what level of specialization or differntiation would be logical in the circumstances and then you see people who are the richest or most succesful not being so specialized. In fact if they are less specialized than their underlings, that is a clear red flag!

On the contrary, it is a good sign. Skilled leaders handle the administrative details and let their underlings focus on doing the actual work. You get to be a top specialist by spending your time and energy mastering your specialty. It just can't be done if you spend a significant portion of your day on administrative tasks. Management requires different skills and is basically a completely different career path from that of the specialist.

This phenomenon was one of the inspirations behind the Peter Principle.