WRT to people saying that Cooper is best used as a decoy: the deal with a decoy is that in order to be successful, they have to present a real threat. In 2014 Dez was demanding a double team on every snap, because if you gave him single coverage, Romo was going to throw the ball there and Dez was probably going to win it. Around 2017, teams started leaving him in single coverage and winning, and as another poster put, it was like the moment where the raptors in Jurassic Park figured out that the fence was no longer electrified.
Honestly, I predict that Coop's going to keep getting single coverage until Dak and him make defenses pay and force a double team. It's not going to work the other way around.