Teams overpaying do not equal the market. Because Haynesworth signed a $100 mill deal doesn't mean every top 5 defensive lineman is worth 80-100 million deals.
Whatever a team pays IS the market.
A player is worth what a team pays for them. Haynesworth was worth $100m to the Redskins, did he live up to it? No. That doesn't change the fact that they thought he was worth it.
Your opinion of the market is irrelevant, it changes every season, it changes with every contract. It's not something set in stone, it's ever evolving.
If we cut Wilfork and someone paid him $20,000,000/yr, he'd be worth it, because that team said so.
A team "overpaying" for a player DOES equal the market, because now other players have all of the leverage in the world, unless all 32 teams united and said "no", but that will never happen, because the types of players we're talking about, the kind that are good enough to discuss "what their market is", will always have a suitor, someone will always offer more than another team.
The only way McCourty plays for New England next season without making top dollar is if he chooses a hometown discount, which he very well may, he is, at least from the outside perspective, a great team player. It's always about the team and not himself from everything we see, however, the fact that he does everything the team asks also can backfire and make him even MORE valuable.