It wouldn't be a good hire from the outset, but we don't know if he would be a bad coach or not. There's no indication that he is a bad coach. There's also no real indication of what kind of coach he would be.
This would be an instance of pretty bad hire, like you said, but unknown on whether or not it would be a good fit and the coach would succeed.
Compare that with the last search four years ago where it was an atrocious hire, the coach was clearly not good and it was clearly not a good fit.
I think Manning would have potential for success, but that we have no idea where the floor is. Bottom line, we should get someone who is better known where we have a better chance of identifying floors and ceilings. Manning is a total unknown.