Managers don't operate like this at well-run companies.

Any remotely healthy team will perform estimation and scoping as a discussion with the developers involved. The author of this post sounds like he has worked at an extremely dysfunctional company, not a company that understands how to develop software.

This idea that managers are universally incompetent just isn't true. The best thing you can do is refuse to support incompetent managers. Change teams or change jobs if you must. There are many, many great managers out there who won't try to pull nonsense like this.