Not so sure that he would have been great anywhere. Brady was disappointed he wasn't drafted by the 49ers, cause he grew up as a fan, but they've been through nine coaches since he's been in the league. No way a quarterback maintains excellence changing coaching staffs every two years.
Agree on your other point. Belichick has a theory that there are a few superstars, but a LOT of people who can perform adequately. He also has an uncanny knack for identifying the lunch bucket guys that perform well enough, and he doesn't have any big holes in the roster. He also jettisons players the second they become a distraction. Randy Moss would have a ring if he'd kept his mouth shut. Belichick will not overspend on any position to the detriment of other positions.
Brady fit into the system, and although most people can't name another player on the Patriots roster, he takes less money than he could, compliments other players in interviews, and is the ultimate team guy.