American sports seem to place a too much emphasis (IMO) on team achievements when assessing individual greatness. Given that Brady accepted a salary under the market rate in order to play with better players it seems like bad way of assessing how good he was. Similarly they love all time lists, which presumably he's going to dominate. I'm not trying to say that he doesn't deserve credit for his longevity or wins, just not the amount that the NFL community seem to give him. To be fair, I don't know anywhere near enough about the NFL to argue the toss about him one way or the other, but the fact that his GOAT status within the NFL or even his GOAT quarterback status is nowhere near unanimous suggests to me that his level of dominance isn't great enough to be considered the second GOAT across all sports.
I have the same trouble with the respect that Bill Russell gets in basketball for his eleven rings is a stacked Celtics team, despite him never averaging 20 points in an offence friendly era and "only" winning 5 rebounding crowns.
To be fair this is true for all sport. Messi's failure to win a major international tournament is a stain on legacy, fairly or unfairly (not saying I agree), and still prompts unfavourable comparisons to Maradona despite being having about 15 world class seasons compared to 3 or 4. If anything I do understand the focus on the individual more understandable in America, as to be fair the quarterback is by far the most important player in an NFL team (especially in this era) in a way that I can't think applies to any other sport, and basketball is a 5 a side sport where it is possible for one player score as much as the rest of his team on a given day (not common, but still). Focusing on the individual is a media driven thing, but both leagues do lend themselves to superstar culture and team achievements are always going to count for more because of that. At the end of the day, sport is about winning.
Older players signing team contracts to give themselves the best shot at winning while they're still playing is a fairly common and well established practice, and to be fair no one was ever going to break the bank for a 43 year old, no matter who he is. Can't imagine money is a priority for him anyway, he's presumably pretty well set after 20 years as the face of America's biggest sport, and his wife is even richer than he is afaik.
Again, I'm not sold on the "not unanimous best" either. You'll find detractors but you won't find many coalescing behind any one individual, you'll find a few arguing for Montana, a few arguing for Peyton Manning, maybe the odd Marino fan but there's no concensus alternative. A lot of the arguments thrown in face are dead in the water after last weekend too. At the end of the day the man has won the whole thing more than any individual franchise, and there's no real arguing with that legacy. To be honest, a lot of the complaints come from the fact that half the league's fanbases have a personal reason to hate him at this point (I'm a Rams fan so I'd know on this one).
I will say that Brady is almost certainly the coolest sportperson under pressure I've seen in any sport, and by a distance. A lot of other things went right, but there's no universe where the Patriots have the same degree of success with someone else there. Going somewhere else and winning gives his legacy a boost it didn't need but does put him in an echelon above every one else, at least for me (and most other people). Similarly, his commitment to winning, and ability to inspire the same quality in others, is something I haven't seen anywhere else. His level of dominance might not necessarily seem impressive at first glance, but the NFL is an incredibly volatile league that has achieved something pretty close to parity. Most great teams last for 3 or 4 years (6 or 7 at a push) do well to win more than one ***le (and there are many who didn't win any, Saints team of the last few years the best recent example). Keeping a team at the top for 20 years is outside any reasonable expectation. Most great players can count themselves lucky to end up with one ***le. Going back to the Saints, Drew Brees is likely retiring this year having only ever gone to one superbowl, and Peyton Manning only won his second in his last season (and that was because of his defence).
This turned out to be a lot longer than intended but oh well.