The Buffalo Bills... aren't that good
The Buffalo Bills look like an elite team occasionally because of Josh Allen. Josh Allen is a very interesting QB. He leads the league in interceptions since entering the NFL but also leads the league in total touchdowns during that time. When he's at his best, there isn't anyone better than him. However, when he's bad, he's really bad.
Between the Bills being 5-4 and enduring a slew of injuries, this team just isn't good. I'd argue the Broncos aren't good, either, but Denver is coming off of two straight wins and surely has some momentum there. The Bills are 2-3 in their last five games. They've lost to Zach Wilson and the New York Jets and Mac Jones and the New England Patriots.
Another issue with Buffalo; what exactly do they do well? What is one thing that they can hang their hat on and say "Yep, this is who we are." To me, there isn't a clear thing that they consistently do better than their opponents. Josh Allen leads the league in interceptions, and their pass game is up and down. The run game isn't anything notable.
And yes, they have lost three defensive starters for the season, so that unit isn't playing as well as it normally does, but even on defense, what do they do well? I'd even argue that the Denver Broncos can hang their hat on an above-average offensive line and a very good special teams unit. To me, the Buffalo Bills simply aren't that good.