It is difficult to build a good football team, where good is one that consistently competes for the championship. I think Belichick knows this better than anyone else. To some extent, the Pats caught lightning in a bottle; no franchise during the time he was coach has been as consistently successful as the Patriots. Every one of the teams that challenged New England during their run has gone through big ups and downs, including the Steelers, Ravens, Giants, Eagles, and Seahawks. Meanwhile, the Pats will win a single digit number of games this season for the first time in 18 years, an NFL record.
Will that happen again? Unlikely, even with Belichick as coach/GM. But I doubt very much Belichick simply forgot how to build a team, or that his philosophy with regards to the characteristics he looks for in players has somehow become outdated. He is not a baseball GM looking for "RBI guys", a basketball GM looking for "a rebounder", or a hockey GM trading for a slow-footed player with "grit". There are a lot of coin flips when it comes to building a football team; the Pats had a lot of those coin flips come up heads in a very big way. Belichick the GM is still the same guy that drafted Richard Seymour, Matt Light, Nate Solder, Asante Samuel, Donta Hightower, Devin McCourty, Gronk, Deion Branch, Chandler Jones, Vince Wilfork, and Julian Edelman. The same GM that traded for Randy Moss, Wes Welker, Doug Gilmore and Corey Dillon. And signed Chris Hogan, Amendola, Darrelle Revis, and Brandon LaFell. And picked up unwanted players such as Malcolm Butler and JC Jackson.
Yes, he had a huge coin come up heads in TB12. And he's had some notable misses as well. And we've seen some of those misses pile up when it comes to the draft recently, a dry spell that every single team in the league periodically encounters (including the vaunted Steelers and Packers).
The current rebuild could easily take multiple seasons; I firmly believe Belichick the GM realizes this. There were a ton of GFIN moves made to maximize the Brady window, and the piper had to be paid this season. But he starts the upcoming offseason with a clean salary cap, plenty of money to spend, reasonably favorable draft position, and potentially a good crop of younger players from some recent drafts. I'm betting heads on this one.