that’s exactly what the matchmaker does, only it’s not always 30 SR because there is not always the exact same average team SR, you get a bonus for defeating a team that has a higher SR than yours, and below 3000 SR there is a performance bonus if you play well (or malus if you play badly)
there is nothing more to it
you get 10 game with 50% chance to win, if you win 5 you end up exactly where you started