I will say this tho...
A part of the reason why a lot of people (including myself) are open to awarding Mahomes the GOAT title is that there are a lot of fans that just don't like Tom Brady the athlete and/or Tom Brady the person and some question the legitimacy of his career.
You know there are a lot of conspiracies and speculations about Brady's career as to why some fans can't or don't want to let go of their negative perceptions and assumptions of him...some people believe he and Belichick (who many don't like for similar reasons) cheated their way to a couple of those Super Bowl titles..deflategate and many other theories plus personality wise IDK some people are not fond of TB12. (or Belichick) for numerous reasons that I can't speak on cause, I don't know what they are.
See MJ is beloved by most fans, it's rare to hear anybody whether it's Bron stans, Kobe stans, or Curry stans, etc who don't love Michael Jordan to some extent. With MJ he was loved so much by fans that he was declared GOAT even before he retired and still to this day it's undebatable to call him anything other than GOAT...
Brady on the other hand is not as beloved by fans which is why his claim to NFL GOAT is being disputed not long after he retired when it seemed like it was set in stone.
Mahomes is reaching MJ status in the sense that he's becoming beloved and adored by fans which is why so many are willing to label him as THE (or soon-to-be) GOAT. He's likable whereas Brady has never been loved to that extent.
Sometimes being the GOAT isn't just centered on career stats, championships, winning, etc (no doubt it plays a big role) but also based on likability, personality, and the perception and connection you have within the minds of the fans. Brady despite his greatness I don't believe has ever reached that level in regards to the fans, which Mahomes has done so far.