I never got this meme. Belichick is a defensive coach. He generally defers to the OC. First Charlie Weis and then McDaniels.
49ners in 2000 had Steve Mariucci, who had broken in Brett Favre at Green Bay, as head coach. They also had Bill Walsh as GM. Two guys with great pedigree in finding and making great QBs. More to the point, the NFC West especially and the NFC generally, sucked in those years.
OTL, the 49ners saw Brady in the 2000 pre-season Hall of Fame game and pretty much everyone on their staff who saw him, has since stated that’s when they realised they should have taken him.
Brady, playing in his home town, for his local team, surrounded by some of the greatest QB trainers ever, in a conference which is pretty weak, yes he would win a metric shit tonne of stuff.