All I'm saying is that performance and pay go hand in hand.
Mankins wasn't cut in 2013. Why? Because of some combination of (1) the team believed that his performance was one line with his contract, and (2) the team did not have an effective alternative at his position.
We don't know that there will be a dropoff at LG this year. It's quite possible that Mankins continues to deteriorate as a pass blocker, and that Kline or Cannon or whoever the Pats put in there ends up developing to be better than Mankisn this year. I understand that the odds suggest that there will probably be a dropoff of some kind, but it's by no means certain, and the team probably has a much better read on the situation than we do. It's not uncommon for aging veterans to get beat out, and teams that keep players based on past reputation and performance seldom have a record of long term success.
The comparison I made was Pittsburgh cutting Joey Porter in 2007:
Steelers cut Porter, Haynes to get under cap - ESPN
Cutting Porter wasn't easy, Steelers say - Pittsburgh Post-Gazette
Everyone thought the move was mainly about money, and that the Steelers were getting weaker by cutting one of their defensive stars. James Harrison was an unknown at the time, and barely mentioned. The idea that the team also knew they had a star in the making and wanted to make room for him was never really considered at the time.
Obviously, we don't know whether the Pats think they have a "star" LG in the making. We don't know their evaluation of their own linemen. Maybe the move was all about money. Maybe Mankins would have started if he had stayed. Or maybe not. But I don't think it's as clear-cut as you say, and I doubt the Pats would have made the move if they considered the dropoff at LG to be unacceptably large.
