Not being penalized for an ally leaving the game.

It's quite simple, if someone who is not in any pre-made group during a game leaves, lets say before the 15 minute mark but after the remake mark, the rest of the team shouldn't have to be penalized when they eventually lose the game. The player who left, on top of being banned should lose something like double the LP one would normally lose. I just went into a game where our adc left like 3 minutes in and never came back, the game itself wasn't terrible, but we eventually lost because we got completely out-scaled in the end. Obviously because Riot loves to pour gasoline on the fire, I got demoted thanks to that game. It's especially annoying when because I was doing well that game and believe we could have won had we had an adc. All I'm asking is for Riot to fix up this shit of a system that barely does anything to penalize the leaver but everything to make sure the rest of the team gets completely fucked over for it. I guess I'm asking what others think, and if beyond the fact that it's not a perfect solution, what would be?