I find it unfair and, quite honestly, stupid to have your MMR decreased because one player from your team abandonned the match, resulting in 4 v 5 or worse.

Even a high MMR player would have some trouble in a 4 v 5 match.

Why not just decrease the MMR for the abandonning player and not their teammates? The winning team can have its MMR increased (be it the 4 or 5 member team). But in case of lose, the team members of the abandoning player should not have their MMR decreased.

What do you think?