The salary cap is a real thing. That statement is heavily debated as everyone has their own idea of how the financial operations of the NFL work. There’s an understanding that contracts can be structured and again restructured to push the money owed down the road, making the salary cap very flexible. Believing in it or not as a real limitation is a personal choice.
For the Dallas Cowboys, the salary cap is a real thing. While they are also pushers when it comes to kicking the proverbial financial can down the road, they are very judicious about which cans get kicked and how far they want to kick it.