IMO, there is no such thing as the GOAT. Brady is one of the best to ever play the game and his being a 6th round draft pick makes it the type of story of which dreams are made.
However, what if the Patriots hadn't picked Brady with the 199th pick? What if it had been the Browns who picked a different QB (Spergon Wynn) with the 183rd pick? Would Brady have been as successful? Would he now have 5 rings?
Give me a DeLorean. Let me go back in time and switch those picks. If Brady is still as successful, then I would agree that he is the GOAT. But for now, I say that he is one of the best. I don't know why that isn't good enough for fans because it sure would make me happy to go down in history as one of the best to ever play a game.