You don’t need all of these additional rules and exceptions. NFL teams are in business to make money, and they’ll budget towards an expected profit or sell and move their team to a market that will achieve their goals. The stated value of the cap being that it increases parity for smaller markets, and benefits the product as a whole. In reality, the quarterback’s value to the team just doesn’t exceed such a great percentage of the cap relative to the other players, and teams or owners will suffer for that encouraging a correction for the league wide value of a quarterback, and that will vary from team to team.
Any player’s value is related to the team’s profit, and it may have less to do with wins, and more to do with appeasing fans, and it’s an aspect that naturally keeps the “copycat” league interesting.