Losing too much LP in games with AFKers and Trolls.

Just got destroyed in a 3v6 game. Our ADC dc'd or just quit at level 1 so our support became toxic and fed on purpose. The 3 of us trying refused to give up so our support would pretend to be ready to tank fights and as soon as 1 or more of us committed to the fight he would back out and wait for us to die or flash away. Then he would go in 1v5 to give free kill all the while being as toxic as he could to us for not being quitters.

When I win matches I typically gain 20-23 LP. If I lose fair and square I tend to lose 17-18. How is it fair that I lose 18 LP when one guy was afk for almost the entire game (adc came back, farmed for a while, went afk several more times, then rage quit in the last 5 minutes). And another guy openly admitted to losing on purpose? The fact that they ruined my chances of winning while also wasting my time is frustrating enough. But losing so much LP from a game that was sabotaged from the start seems overboard. I am sure there is an easy fix to this... Maybe adding a code that sees when a player is standing still a lot or notices when they have extremely low damage (e.g. our adc had 1,500 damage after 23 minutes). And a code to notice when players are consistently feeding the enemy. I understand that in some ELO's the feed is strong and normal but around gold and up it's not normal for an Alistar to die 9 times all of which were when they were alone walking in circles while the enemy killed them.

The frustration caused by trolls in ranked this season is more than I have ever experienced in all the time I have played league of legends. I am sure there are some smart tricks to curve the frustration by simply adding some sort of extra LP loss for the trolls while decreasing the penalty on the players who try hard.