IMO it's a "2 way street" at the signing of a contract. The team, the player, and his agent know - or should know - all the advantages and disadvantages of the contract being offered. Here, according to rotoworld’s site are the terms of the contract he signed: IMO the major risk the player assumed was outplaying the terms of the contract. The major risk the team assumed was a career-ending injury as well as the risk of the player under-performing the deal.
That’s the 2 way street.
Rotoworld goes on to quote Rapoport: That isn't a huge difference but he agreed to the contract in place knowing (or he should have known) there was a chance he would outplay that deal. And he was guaranteed $17M even if he suffered a career-ending injury in his first practice of TC in 2013.
BTW, Sky King: I agree with everything in your post except your posting “He's led his team to more Super Bowls” is technically a fact. (If you hadn’t said technically I’d have let it go
) The fact is he was the quarterback on two Super Bowl appearing teams. To the extent he “led” those teams is an opinion (technically).