This is a big "grey area" subject where who is right might never truly be decided.
Yes it's true that NFL players make a lot of money. But that does not mean that they should be denied the right to seek more compensation when they feel their contribution exceeds the amount stipulated in the contract.
Just think of how many Fortune 500 CEO's made loads more money than the highest paid NFL player. Yet they can leave thier job at will, usually so long as they do not leave to a direct competitor. Oh they'll say it is for a "new Challenge" or "opportunity" But usually it is for more money or more power. And Most CEO's sign multi-year contracts too.
The problem is that NFL players cannot just up and leave their organizations to go work for another one. They can't go to another NFL team as the contract to their current team would need to be traded. they can't go to a differet industry. Other than the CFL, there is no market for their talent. And they can't resign as they will risk losing their operating form and peak fitness. Thus losing their market value.
Also, No NFL Organization is going to give more money than the amunt stipulated upon unless asolutely made to do so. Which is perfectly respectable. No one expects any company in the US to increase compensation to a worker without the worker's request for a raise (and the implied threat of the employee leaving if the request is not granted). We shouldn't expect generosity above the US Norm from NFL Teams either.
Sadly, the only recourse for a NFL player is to sit out the training camps and hope that the Team powers that be agree to their terms before the lack of practice is a detriment to their contributions and abilties.
I do agree that this Rosenhaus fellow is setting up his players for a bad ending. It's practically impossible for this one agent to have as many players (as he claims) performing so far beyond the levels stipulated in thier contracts that they need to sit out on practice in order to be heard. No one will be black-listed. But I'm sure there have been players who were let go for less than what Rosenhaus is having his players do. And once their current contracts are up, It is going to be very difficult to get a faircontract for these players, as they will have a history of renegotiation.