You'll note that the Patriots are joined by the bottom feeders of the league, like the Browns and Ravens, because injuries typically play a large part in the success of a team. The Patriots have roughly twice the injuries of the top teams in the NFC, and nearly thrice the injuries suffered by the Bengals and Broncos.
If you can't find the Bengals on the chart, they're the tiny dot to the left of the Denver dot. The circle size represents the quality of players lost, and Cincincinnati's circle is small because the Bengals haven't suffered from any major injuries this season- until they lost quarterback Andy Dalton.
The Broncos circle is large because the metric inflates the value of Peyton Manning, by comparing his value from prior years. Manning ranked as the worst quarterback this season, so his loss wasn't that great. This metric also greatly undervalues the impact of Dion Lewis, because Lewis was out of football in 2014.
The bottom line is that one of a few things should happen. Either 1) quarterback Tom Brady deserves MVP for playing alongside all of these injuries; 2) head coach Bill Belichick deserves Coach of the Year for managing all of these injuries; 3) general manager Bill Belichick deserves Executive of the Year for creating a roster that can win in spite of all of these injuries.
Hopefully players get healthy so the Patriots can lose their #1 ranking in the coming weeks.