Can't equate caps across the board, the Cowboys are heavy O but a team that is heavy D could easily manage a 20M WR contract if he fits their offense. It is not lost on other GMs how Cooper helped this young QB. There are others that need great route runners.
Cooper's trade value is directly proportionate to his consistency and not disappearing during games. That, no team will want. That is how the Cowboys ended up with him. But if being doubled can excuse some of that inconsistency, that's different and there's not an OC in the game that doesn't want a WR that can pull doubles.