Sherman was a good coach but didn't have a handle on Favre. Those were Brett's lazy years where teams rightfully didn't respect him. However, they were downright terrified of our running game. Without Ahman Green, one could argue that Favre's career would have ended before he got to the McCarthy years. Sherman drafted three offensive linemen in his time as GM, only one of which (Scott Wells? - I'm going off memory) panned out. TT got here and inherited two quality guards looking for big money in FA, and no young talent waiting in the wings. Sherman gets credit for maintaining a highly competitive team. As dblbogey stated, Harlan gets the blame for thinking that Sherman could handle both roles effectively.
My boss has a house on Cape Cod that abuts the football field where Sherman coached. My wife and I were out there a few years ago and we walked over to see the game on our way to the beach. I was shocked to recognize Mike Sherman and confirmed it by looking up his coaching gig on my phone. There's not much of a year-round population on the Cape. I can absolutely imagine that it's hard to field a team.