The Cowboys had more time to prepare and the advantage of seeing how other protest methods would struggle, but their choice seems to be best so far: effective and unified protest without denigrating a symbol that is **sacred** to so many people.
The lack of empathy on both sides is noteworthy. (In recent months, we've seen some on the Right struggle. Here, it's many on the Left in general [the more common problem a la Haidt].) Failing to understand how their protest could be so easily misunderstood. ("Oh, I didn't mean that!") Failing to understand the perceived sanctity of the religious symbol and the necessary/obvious fallout. (If I have a problem with African-Americans, how would it be perceived for me to denigrate MLK Jr. symbolism in some manner?)
Confusion over "free speech" is another problem. You're free to say what you want. (The govt ain't cranking on you, bro!) But private employers may find you personally bothersome (or attractive) based on your speech. And they may certainly find you a production-decreasing distraction to their teams and their teams' fans. (See also: Tebow, Sams, Kap, Rice.)
In any case, all of this will accelerate the NFL's decline, for better/worse. Wealthy professional athletes will not get much sympathy here. (Be careful, NBA!) NFL athletes will get less, given the shenanigans in their league AND their silence or defense of same. And people have substitutes-- in sports and entertainment.
Maybe Trump is trying to make hockey great and make baseball great again?