Allow Loss Prevention/LP when it is 4v5 in ranked games
Only punish the AFK/Leaver with the loss they created. Create a report option that requests a loss prevention for it being a 4v5 game. and only show the level of the champs played. If 1 player is 10 or less and everyone else is 18. The losing team deserves a loss prevention.
If you WIN as 4v5 then you should get bonus LP due to winning and still being handed a sour hand. and the AFK/Leaver should have the win removed from their record since they did not deserve it.