I used to work as a manager (of managers) and I did like 4 different jobs at once in that role, and most of this was because I managed a drooling retard (who also managed drooling retards) among two other people (one was great and the other was okay). It's true that I did almost nothing for the good manager since she had shit on lock.
Now I'm in another role at the same company and I'm pretty sure that the guy who replaced me doesn't do much aside from 'managing.' there was also a counterpart of mine who did hardly anything himself and just shit out opinions and half baked ideas
Tl;dr, it's pretty true what you mentioned about management in my experience, but my company also isn't some well oiled machine