It is common knowledge that he is on the non-exclusive Tag. That was covered in depth back when they first tagged him. Any team can sign him if they want to give up 2 first round picks. That can happen up until July 15th. Now that the 2015 draft is over, those picks would be 2016/2017 which is even better for a team that might want him that it was before the 2015 draft when they would have been required to give up a 2015 and 2016 pick.
Calvin Johnson at the time he signed his contract was the undisputed #1 WR in the league. Dez is not the undisputed #1 WR in the league.
That fact that the Lions went nuts and overpaid CJ is not proof of the market value of other WRs.
The Cowboys don't have to agree to anything in terms of not Franchising him next season. He really have not significant leverage.
It does not seem fair that Zack Martin is an All-Pro but is getting paid 2.2M average while a far inferior player like Doug Free is getting paid 5M average. That is how the system works. The Franchise Tag is part of that system. Poor ole Ron Leary was terrific last year and was part of arguably the best OL in the league and he only got 500K as an ERFA this season.
If you really want to get in "fair", consider all of the people that developed the technology that we all use today. Personal computers, the internet, smart phones, tablets, etc.,. etc. The vast majority of those people, despite being in the upper 20% of intelligence relative to the worlds population, probably averaged less than 100K per year while developing all of that great technology. That's just how the system works and they've accepted that athletes that score a 6 on the Wonderlic get paid millions before they ever prove anything. That's how the system works. I'm sure most of those people do whatever they can within the rules to maximize their own pay; however, I don't think they go around crying that it's communism.