Cowherd is not much different than other talking heads who say things just for clicks. He probably doesn't believe it himself.
Stafford was under appreciated nationally while in Detroit. You could argue his prime years were wasted and the perception of him would be much different, if he hadn't been drafted by a franchise rebuilding from the ground up.
Rodgers is a top 3-4 QB of the Super Bowl era. In far as what actually has happened, Stafford isn't eclipsing him.