They won the Superbowl played in January, 2017, lost the Superbowl played in 2018, and won the Superbowl played in 2019.
I mean, seriously. So, after that February, 2019 SB, you had a team full of guys who had played more games, longer season, grueling pressure for three straight years. And a team full of guys very likely a bit less hungry, because that's how humans operate. You also, for 3 straight years, had FAs who were going to get ABOVE market, as SB FAs almost always do (EDIT: and coaches!). It also means that for 3 straight years (and really, for 5, rolling in 2014 and 15), you had very deep VETERAN rosters, because that's what SB teams usually have. This also means lower draft picks, round after round (not counting the stolen ones).
Not a lot of rookies start on SB teams.
There's a price to pay for 5 years of that kind of NFL dominance, individually and as a team. Loosen the leash a bit here on BB and the Pats.
2019 fell apart with Gordon, AB, Sanu getting hurt, Brady having clearly had enough. They were still a playoff team, which many cities would kill for. They were trying to squeeze out one last run, but it fell apart - Gronk retiring before the season AFTER any half-decent replacement could be found; Gordon falling apart after 6 games; Antonio Brown bringing his freak show into town and completely screwing up in short order; Sanu getting hurt right after coming here.
2020 was a complete reset, more than typical with the opt-outs. It was all about cash, Yes, I think, in hindsight, that Thuney and Gilmore were errors. BB wanted to keep Thuney, but he broke the bank with a desperate SB favorite. Gilmore is a different story, as I believe BB was hoping to got another deal done with him and would have paid it if he held up to 2018 performance levels and hadn't gotten hurt.
The reset is over. That's why they brought in a new core group, hoping to rebuild that middle class hollowed by the 5-year run. And now have added the new centerpiece, who's a rookie.
If they're under .500 this year, that'll be disappointing. If they can't get to playoff contention next year, then it's time to think about shortening that leash. I think this is a pretty good football team that needs to correct a few things that seem correctable. Which is kind of remarkable given the turnover.