With the Tom Brady era over in New England, it's worth trying to determine how much of the Patriots' dynastic success was due to their membership in the subpar AFC East. As a coworker posed it, what kind of an advantage did the Patriots get from basically being a playoff shoo-in every year? With an average to above average team, making the playoffs over a 20 year span, how many Super Bowls would they expect to win?
Looking at their last 19 seasons (once Tom Brady became their starter), the Patriots made the playoffs 17 times, winning the division each of these times (the two seasons they missed, they lost the wild card on a tiebreaker). They won 30 playoff games, made the Super Bowl 9 times, and won 6 of them.
Getting in to the postseason 17 times certainly is a huge advantage, so to quantify this I estimated how the Patriots would have done as a "generic" playoff team, with the home field advantage they were granted every single time as the AFC East division winner. They never made the playoffs as a wild card.
As I found earlier, playoff home field advantage (4.35 PPG) is a bit higher than overall (2.41 PPG). Converting this to a win probability, between two evenly matched playoff teams, the home team would have win odds of 67.11%. When the Patriots were a 3 or 4 seed, they were guaranteed one home game; as a 2 seed, two home games; as a 1 seed, three home games.
I ran this math out over the past 19 years of the Patriots dynasty: