Bill has coached 10 seasons without Tom Brady, six before Tom and four after Tom. Only two of those were winning seasons. His record those years was a below pedestrian 70-93 for a wonderful .429 winning percentage. His playoff record was 1-2. Not saying he isn't a great defensive mind nor that he is not better than McCarthy, but Tom covered a whole lot of his warts for 20 years and then went and won another Superbowl without him (making the playoffs all three years with Tampa while New England fell apart).
I think looking at the actual history and coaching statistics from an impartial point of view, you would have to say Bill would probably not sniff the hall of fame if Brady never saw a snap. Heck he may have been on his way to getting fired from New England (since they were 5-13 in his first 18 games as New England's head coach before Tom took over) and been stuck as a DC for awhile.
You want to talk about coattail riding for McCarthy with Rodgers, well it is on steroids for Belichick with Brady.
McCarthy with Rodgers: 106-44 .611
McCarthy without Rodgers: 66-43 .606 (including this season)
Belichick with Brady: 397-173 .696
Belichick without Brady: 70-93 .429