The Cowboys have one of the top 4 quarterbacks in the history of the NFL. His stats are undeniable and (unfortunately sometimes) he has the balls to take chances. Nobody complains when he wins, everybody complains when it doesn't work out. But look at the stats.
Manziel is an awesome high school/college QB. Like Tebow, McCoy, etc., his style will not translate well to the NFL. You need to know how to use your assets... you won't get away with being a mediocre quarterback and making up for it with scrambling like you can in college.
Manziel is now going to disappear just like McCoy and Young did.