How does a 4v5 not permit a loss prevented?
I totally understand that a duo partner could just leave and you wouldn't lose lp, but they would, and they'd also probably get suspensions. Why would someone even be willing to do that? You should REALLY be awardess loss prevention for afk's. a 4v5 is a complete disadvantage and if your matchmaking system pairs up two about even teams, it becomes VERY uneven when a player from one of those teams leaves.
I just played a game where our top laner dc'd 4 or 5 times for like 3 mins each, was barely there half the game. He ended up dc'ing at a dragon fight twice and in a different team fight another time.
Its completely ridiculous that players have to lose LP just because other players can handle their temper or they play when they have awful internet. Every single game man.