If a QB struggles to put up 300 yards either he isn't very good or the coach likes to rush 30-40 times per game.
You might not like it, but the 300 yard game is a genuine measure of success if winning games is the correct measure of success. According to Statmuse the top 25 quarterbacks for 300 yard passing games in 2021 had 102 of those games. Of those games 61 were won and 41 were lost. Most 300 Yard Passing Games By Qb 2021 | StatMuse 300 yards passing is not going to be enough on its own to make lousy teams win (see your Winston reference) but it cannot be denied as a significant benchmark.
If your defense sucks you ALWAYS have the ball because the other team can score at will giving the ball back to you.