Analysis by BBC NFL reporter Ben Collins
McDermott ended an 18-year play-off drought in his first season with Buffalo and helped them become post-season regulars, but the Kansas City Chiefs proved to be his nemesis.
The Chiefs have knocked the Bills out of the play-offs in four of the past five seasons, on the way to establishing a dynasty that produced three Super Bowl wins.
With the Chiefs failing to make this season’s play-offs – along with AFC rivals Baltimore and Cincinnati – the path was supposedly clear for McDermott to lead the Bills to their first Super Bowl since losing four straight from 1991 to 1994.
But while this was McDermott’s best chance yet, the Bills’ roster was their weakest since Allen was drafted in 2018, and it was relying too much on the NFL’s reigning Most Valuable Player to keep producing moments of individual magic.
The re-emergence of New England meant the Bills relinquished the AFC East title so had to settle for a wildcard spot and go on the road in the play-offs.
And despite winning at Jacksonville on Wildcard Weekend, they came unstuck in the Divisional Round at Denver.
Buffalo became just the fourth team to win a play-off game in six straight seasons. A telling fact for McDermott is that the other three teams all claimed three Super Bowl wins during those runs.
He and Allen, on the other hand, have the unwanted records of winning the most play-off games by a head coach and quarterback (eight) without reaching the NFL’s title decider.
At 29, time is still on Allen’s side. The Bills are about to move into a new stadium and some high-profile coaches have come available in the latest hiring cycle.
So the team felt that by acting now, it allows a new coach to rebuild the roster and gives Allen the best chance of leading Buffalo into a new era that finally delivers a Super Bowl win.