Win 30pts loss 30pts

it doesn’t

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