You know, we won the game. So you got elo without even playing. And including you (who could have rejoined) only 2 of 6 players quit, that's not half the team. If the weaker team really wants to exit, they can just quit.
Anyway, elo increasing or decreasing is not a bad thing. Not at all. It helps balancing future games. I really don't understand what you are complaining about.