The quality of players isn't determined by how often they rematch because the majority of people who play this game are uber casual, where they don't even know bo3 or bo5 is a thing. Your entire perspective is wrong if you don't realize that we here are the minority.

The quality of the average non-Elite Smash player is as shit as it has always been. Because they are literal casuals. They play to have fun where their meaning of fun is vastly different than our meaning of fun.

Also I have seen exactly 0 cases of this type of alleged quality decrease leading to a dead game, especially in a game where the majority of the playerbase has been this quality from day 1.