Ranked LP

I'm sure I'm beating a dead horse in its grave and this topic has come up a hundred thousand times. So maybe I can be enlightened.

But why is the ranked points system in solo que so terrible and imbalanced.

And by that I mean why do I lose points for a teammate going afk or for a general loss when I do very well. I've had games where I go 9/2/7 with good cs for example and a leaver will cost me a match and I lose LP. If anything if a person leaves the game and that team loses, the rest of the players on that team shouldn't be penalized. The other team should still get their lp that they earned through winning of course. LP should be based on performance IMO not win-loss. I know that his could be abused in some ways but it just doesn't seem Ok that other people should be penalized for another's mistakes or poor choices. Why not use the Character performance grade as a way to determine lp? Clearly they have a way to determine that so I don't think creating a new system would be that difficult.

Again this is probably a conversation had everyday but I am just looking for an explanation or answers.