People can grow into their roles. You don’t expect junior devs to know everything one day one, so why would you expect a “junior[1]” manager?
[1] I know the article is about senior managers, but it reads as though the mean “somebody more senior than me” and not “somebody who has been managing a long time”
The difference is the damage done.
I don't think training managers on real people is a good idea.
Genuine question: how do we train managers, then? Surgeons have pigs, but even then it's not perfect, and there comes a point where they have to perform surgeries on actual humans (hopefully under supervision).