I see your point and am not denying Sullivan's importance. But at the same time, it would be like saying James and Deloris Jordan are the most important people in the Chicago Bulls franchise because they created Michael Jordan (sure, that's an exaggerated example, but I love exaggerated examples). Without James and Deloris, there is no Michael Jordan.
3 Super Bowl rings ago, Sullivan would have been top on the list along with Kraft/Parcells/Bledsoe.
But the franchise has been re-defined into the premier sporting franchise of this decade, a model upon which all other sporting teams in every sport aim to achieve, and the three most important people in doing that are Brady, Belichick and Kraft.
If I asked you who the three most important people in the history of America, who would you come up with? The first colonists who came here, or any of the great men who made the country great in the centuries after that? Again, greatness is more important than existence.