Brady is a unicorn in that he is elite in all three ways that matter:
- His peak performance was absolutely elite. 2007 was one of the best seasons any QB could possibly have had. 3x MVP, 4x 2nd place MVP, 2x 3rd place MVP, 1x 5th place MVP, so 10 times he was in the top 5 in MVP voting - insane. Led the NFL in key passing stats (pass yds, pass TD, passer rating) 12 times. I think other QBs have had peaks that are as good, or even better, than Brady, but Brady's peak is still one of the best ever.
- His career compiled stats are obviously elite. This is where playing for a long time clearly helps. But he's put up mind-boggling career numbers. He is #1 in NFL history in this category.
- Winning. Whatever dispute people may have about comparative talent, or individual awards, or whatever, one thing is not up for debate because it's objectively true, is that Brady is the greatest WINNER the NFL has ever seen, by a humongous margin.
So Brady is the greatest ever in two of these three categories, by very, very large margins. And he's inner circle elite in the other one. That's a heck of a lot for someone else to overcome. So far, Mahomes is right with Brady in terms of peak (might even be better than Brady), but he's got a long way to go for the other two.