I think it's kind of hard to apply standard skill based matchmaking on something like rush, they are looking for 8 players out of however many are online at one time, then you add in the fact that people like me are turning crossplay off restricting the amount of players available in general.
I really do understand your frustration with the mode though, the amount of people that just want to go off and do their own thing, don't select a player towards the bonus points, or just rubber band to the edge of the pitch is ridiculous. Don't get me wrong I'm far from the best, but the amount of players that don't understand basic positioning, or even to take the open pass for an easy goal is just stupid. It's a complicated situation, but the only other option would be to change it to a 1v1 mode with AI goalkeepers, and only make goal objectives and or something similar.