You are describing the best kind of manager for two reasons:
1. They understand what their reports do, can mentor the less experienced ones, and are a competent peer to the more experienced ones, rather than an obstacle.
2. If they turn out to be bad managers, there is a low stakes, no hard feelings, path for them to go back to being an IC. There is a huge aversion to firing people, so bad managers who can't do anything else tend to stay around creating problems much longer than bad managers who can also contribute.
Your presentation of "experience" and "preparation" as the most important things for a manager is typical gatekeeping that we see from the bureaucratic class--parasites without any real skills.
Strange that you’d say that. What I’ve seen is that promoting homegrown ICs to line management is a favored strategy of nontechnical MBAs in upper management. Any large organization is bureaucratic. Given the intensely bureaucratic record of communist governments, your invocation of Marxist rhetoric here is frankly laughable.
What promoting inexperienced managers from within does is place them at a tremendous informational disadvantage. Never having worked anywhere else, they don’t understand the coded language of bureaucracy and they have no perspective on what constitutes normal behavior. This gives the MBA latitude to abuse them as pawns in organizational power games they don’t understand, until they either burn out or wise up.