I would agree with you except for the legions of god-awful managers I have encountered. A good manager is a huge asset for a team, but a bad (or even mediocre) manager is often worse than having none at all.
That's what I meant too, a good enough manager is an immense value, the others are nothing and are probably only there because somehow humans/societies recognized how crucial and applied 'put a manager' everywhere without care.
But yeah you're right a bad one will turn a team comatose.