Chase Claypool was traded for a 2nd.
Tyreek Hill brought 5 picks including a first and a second. AJ Brown brought a 1st and a 4th. Cooper was already under contract for 4 years at less than what these guys ended up signing for with their new teams.
Calvin Ridley brought more than Cooper. Kadarius Toney brought more. Jalen Freakin' Reagor brought more.
I have no idea how you've talked yourself into thinking the Cooper value was comparable to other WR trades from the same year.
I'll say without hesitation that they sold low on Cooper, but that doesn't mean it's not what the market was at the time.
The Tyreek Hill trade was insane, but he's also a unique talent (1700 yards last year), and the Dolphins had the luxury of signing him to a new deal that fits the structure they want which I think is a huge piece when talking about trades. Same with Ridley which I believe his deal gets bumped up to a higher pick if the Jags can resign him, but I need to look into that. The Claypool deal was an overpay IMO, but rookie deal and an in season trade. Kadarius Toney...rookie deal.....Jalen Reagor....rookie deal....still not like Toney/Reagor went for big bucks though.
The issue with the Cooper trade was twofold in that the Cowboys had both money and timing working against them....a large contract during the start of the offseason, when cap space value and draft pick value is at a premium. You trade for these receivers while they're cheap or when you can create the contract to fit your team and you'll naturally pay more for them. Trading for a guy coming off a 60ish catch 800 yard season who you have to immediately restructure to manage his cap hit isn't sexy to teams. Had the Cowboys kicked in some cash to the deal I have to believe they could have gotten a better draft pick, like Chicago did for Robert Quinn this past season, but who knows for sure.
Personally, I like Cooper and would have preferred that we just kept him over dealing for peanuts, but I can see why he wouldn't have much of a market given the time of the trade. The Cowboys flipped the script this year and took advantage of lower trade value snagging Cooks/Gilmore.