I guess when I see "perennial contender" I think of a team that has a reasonable chance to compete for a Super Bowl.
That was not the 2017 Bills. That was not the 2021 Patriots. That was not the 2019-2025 Steelers.
The window for perennial contender is opened by a QB, not a head coach. Which is why despite McD/Tomlin and the greatest coach of all time, those teams weren't serious.
The reason the Bills have a reasonable chance to compete for a Super Bowl, every year, since 2020, is because of the guy wearing 17.
Give McD Mac Jones and semi-retired Cam Newton, and he can make some 8-9 win magic and get blown out in the WC round every once in a while for sure. Woo hoo.