This is a forum theory with no basis. If you are an active player, winning a game gets you about 19 SR. Losing a game costs you about 19 SR. Performance is a small modifier on top of that, just like the regular season.
See How Competitive Skill Rating Works (Season 11) → Season Transitions for more detail.
Regarding leavers: you don’t get any special consideration in SR (or otherwise) for leavers. See the section on the Leaver Penalty.