They each benefited from each other, but a receiver or tight end's success is obviously dependent on QB play. And Romo was running for his life most years, playing behind lines riddled with Phil Costa, Pat McQuistan, Ryan Cook, Nate Livings, Derrick Dockery, Alex, Barron, Kevin Kowalski, David Arkin, Montrae Holland.........it was musical chairs.
Who has Dak made better? Does he have a Laurent Robinson, Terrance Williams, Sam Hurd, Miles Austin, Patrick Crayton to his credit? Romo made those average guys more than average. He got each one of them big paydays. Cooper is a very good player who just needed a better team and change of scenery from Raider hell.
Dak needs perfection around him. He needs every body healthy. Then, he's pretty good. But if the run game is faltering and Tyron Smith is missing, Dak turns to goo on a shoe. He's looks castrated on the field.