You would probably always argue that a project will generally suffer if it has a hapless buffoon of a project manager. Strangely, this isn’t always the case.
There is a particular type of hapless buffoon that knows he is out of his depth and is open to suggestion and instruction. A project that has a strong technical team can get the right thing done by telling the project manager what to do. The manager does the dull stuff, goes to the meetings, sorts timesheets etc, letting the team (or lead individuals within the team) make the major decisions and get on with the work.
Teams who work for such managers can enjoy a great degree of freedom and success if they realise that the ‘leader’ is easy to manipulate in this way. Keep and eye out for them, you might be missing a trick.
Obviously, the hapless buffoons that linger under the misapprehension that they are in charge and should make the decisions themselves will always cause a disaster.