The NFL would have been fine with, and actually preferred, no appeal . The point of an appeal is not to do the investigation again, but to hear and respond to the punished player's arguments that it was flawed. Brady apparently did not want to contest the McNally and Jastremski testimony and evidence.
What I don't understand is how Brady can be punished, if he is, with not making those two available to the initial investigation. That is not his responsibility, is it?