So the Patriots have dominated the AFC East since 2001. Only in 2008 (Brady missed Year) did the Dolphins win the division after winning the tie-breaker between them.
Now Tom Brady is 42 today and will be 43 by next season. After a weak receiver core all season, the talent of Brady wasn't enough to get out of the 1st round of the playoffs or deafeat the Dolphins to secure a 1st round bye the previous week. Now the BIlls have emerged as a comptetive team to put the Pats on the ropes. The 2019 Dolphins went from "one of the worst teams of all-time" to a 5 win team and beating the pats, The Phins have 12 draft picks in 2020 and 8 in 2021, they hope to be back in the running very soon. The Jets are a question mark from year to year, could be good, could be bad.
No one is saying the Pats have no chance to continue to be a very good team. After years of almost 6 wins in the bag from year to year is over. As well as father time is undefeated and 43 is still 43. Add the lack of offensive talent (can be fixed in the off-season) they don't seem to be the same formidable team that the league is accustomed. So now that the Pats have shown shown rust on ther armor, the AFC East may finally be entertaining again after 20 years of Patriot domination.