Lets just separate his playoff performance from his contract for a minute.
There is a reason agents and the players unions in every sport wants their players to 'set the market' for everyone else, it's called a comp. Basic of supply and demand. If your agent can paint a picture of you that shows that your similar to another player, and that player got X, a team cannot just go and say 'well that's an overpay, we don't believe the market for that caliber player is that' without a back up plan which in football only consists of younger players who are paid on a rookie scale.
If they don't have that, and they, say, go on the open market looking for one......how, exactly are they going to find a BETTER QB, for less money than the one they let go???