Assistans aren't quite the same as managers. People managers manage people, help them get wider perspective on their work, pursue training opportunities, monitor performance, connect with relevant coworkers, and make decisions related to keeping the larger team moving in a common direction. That is a valuable skill, but a level N $x-earning contributor doesn't need to be people-managed by M>N $y > $x
Check out the "skunkworks" model for similar examples.