> The greatest movie critics probably can't direct or write for crap
They may know a lot about how a film is made. It does not follow that they could sit in the director's chair, or write a decent screenplay. (And yet, they could still be great at critiquing films!)
This is a valid point. Just knowing how something is made doesn't necessarily mean you know how to make it. It's the difference between a designer and an implementer. Or architect and builder.