Are you under the impression he was, like, a hands-off project manager or something? His involvement was in writing it. Not singlehandedly, but certainly as part of a team. He unquestionably wrote it. He did not envision it like he did the other projects you mention, but the original credit was only in the writing of.

To say "Rob Pike wrote Unix" is completely inaccurate. He joined after v7, in 1980.