I like the logic in your post.
IMO, calling Brady GOAT is an apples to oranges comparison with guys like Marino, Elway, Kelly, Montana, etc playing in a different era with different philosophies and rules; just not an appropriate comparison. I do think NE is the GOAT pro sports franchise. What they have been able to do in this era of FA is remarkable since it is harder to hold onto good players and stay within a salary cap. They seem to value a core: Belichick, Brady, Gronk, Edelpunk; the rest look to be plug and play. They are good at evaluating a player and determining if the player can fit into the system and bringing out a player's strengths.
It will be interesting to see how they'll replace Gronk, if they even can, since his physical skills are really deteriorating. Win or lose (which I really hope they lose) this is not the end of NE. I don't think they'll be done until they're like 6-10 and Brady is getting pounded by the opposing defense. This could take a few more years.