Exactly this. Making the line $20 million dollars is arbitrary. If you don't normalize the data to show correlation to the Cap, then $20 million is essentially meaningless and ultimately coincidental. With more players making $20 million dollars a year, that imaginary line could disappear as early as this season.
Probably should focus more on the idea that the Super Bowl is extremely hard to win. Only 33 quarterbacks have won a Superbowl in 54 years. Think about that, without digging too far into it because I am not bothering to see how many Quarterbacks have started a game since 1966, I am also not going to see how many teams played per year. But, on just a simple math the likelihood a given team will win a Super Bowl is 3%. Like it or not, the window is always going to be small, whether you pay a Quarterback or not.