As we sit here today, there's little question in my mind that Darnold is the real deal. The main question at this point is how he handles the success, notoriety, expectations, etc going forward. And sure, he could end up getting seriously injured, like Rosen, and that could derail some things too.
As for Rosen, I think he is or was a stud, but he chose the wrong offense to play in and coach to play for and now has to overcome a significant injury to his throwing shoulder.
