Oh, I don't know that I agree. Look what happened to our Chiefs...from a last place team to a playoff team in one season. I don't think considering today's NFL it's possible to predict 100% which teams/divisions will do well or not. Teams make so many changes during their off season, anything is possible from them the next season.
Also, I will not root for a team to win a playoff game simply because they're a division team...never have, never will. If the Chiefs aren't in the playoffs, I choose which team to root for based upon many factors. I don't always root for an AFC team to win SB either, sometimes I'm partial to the NFC team, for various reasons.
I can only remember rooting for the Raiders once...the year Gannon led them to the SB. I have NEVER rooted for the Bronco's, and likely never will, haha. I did root for the Chargers several years ago when they were up against the 49er's in SB. I rooted for them too in playoffs KC wasn't in, most recently when Marty was their headcoach.