Bills have built their team to beat the Chiefs, they viewed the Chiefs as the big brother in the AFC that had to be taken down. That is one of the reasons they struggled some with power running teams this year (Indy, Tenn, NE), their personnel is somewhat ill-equipped to deal with that because of how much they're built to beat the Chiefs who are the opposite of those teams.
KC's OL is better than it was last year with the additions of Humphrey, Thuney, Brown but the advantage they had was they had the best TE and 1 of the best WR's. Can't play man vs Hill, can't play zone vs Kelce....I think both of these guys have comeback to the pack some this year, Hill because of injuries/defenses taking him away more and Kelce because of age. Their offense just isn't as explosive, Pitt is not a good team and didn't belong in the playoffs.
Think Bills D holds up a little better and their weapons are a little younger/better with Diggs, Knox, McKenzie, Davis.
Week 5 wasn't everything, no 1 game is but it wasn't nothing either
Think Bills win SU