Well we all can pick a number.
6%? 19%? 15%?
I suppose it depends on the team and the offense. Definitely not more 20%.
Yes we can and you have undervalued it and no one agrees with you teams don't pay the quarterback The Lion's share of the cap because he has little impact on the game.
Get a grip and look at the way the league stands today the quarterback is more important than ever because it is a passing League it used to be running backs had way more value