It is still a bit early in Brady's career but boy he is off to by far the best start ever. Certainly already a hall of fame career in my view but if he had a career ending injury this weekend, I not sure he would be quite among the best ever yet.
Sandy Koufax is considered one of the best despite a short career and less than impressive career stats in terms of wins. The same holds true for Gayle Sayers who spent only 6 years in the NFL. Brady is one of the best regardless of what happens.