I'm not saying Payton isn't a good HC, he is. We will find out just how good when we see if he can rebuild the Broncos or win with what they have. But sustaining success for 15 years and even winning one Super Bowl, takes the combined talent of the coaching staff, players, and the front office. Sometimes a synergy develops that just works and it's hard to recreate that synergy in a new location. I suspect Sean is seeing that now.
Edit: I'll add that the Saints are seeing how hard it is to maintain that synergy when you lose one or two of the key people in it. They tried to re-create that synergy with the same front office, mostly same players, and mostly the same coaching staff. But, it just doesn't work without Payton and/or Brees.