Reporting feeders doesn't work
One match we had an autofilled support Garen that trolled the entire match, didn't buy items and finished with a KDA of 1/16/0. I reported him and even wrote a ticket to Riot describing exactly what he did. In response they told me to report him and they pretended to be sorry for my terrible experience. He wasn't punished in any way.
About a month ago I reported a Master Yi jungle that forgot to take smite, started ancient coin and rushed dead man's plate before getting three dark seals. His KDA was 1/6/0. I reported him and I expected to see him punished but he didn't receive any penalty.
Recently I reported a Shen because he wrote "KYS" in all chat. Five minutes after the match I received a notification informing me that he got punished. Feeders bother me more than flamers because I can mute flamers but I can't make feeders not feed.
In conclusion, feeders should be punished as harshly as flamers.