It is not just the playoffs that were tough.
I believe the Bills had one of the toughest regular season schedule in recent history... They were pitted against the NFC West lined up with elite QBs or superb defense and were a miracle catch away from a 4-0 drubbing. They played the most competitive 2nd seeds in the Steelers, Titans and if not for a confusing covid situation would have been a 2-0 score. Agreed the AFC East was in a transition and the QBs of Dolphins, Jets nad Patriots were nowhere to be found, but they all played tough and every win was hard-earned. The Bills have won every single game post that hail murray with a margin of 10 points or more except the playoffs against the Colts
The Chiefs on the other hand have played the aging NFC West, a really nondescript AFC West and a AFC East that only had one QB to be found. Yet they had zero wins where the margin was above 10 points
And remember that Allen was wearing the shoulder harness in both the early losses.