Instead of Only Punishment, Why not Reward?
Yes, I know, there is a rewards program to give you a fancy little banner around your loading screen. However, it's not used. The only time I see them is when I play with friends who I know only play with other friends, so they reward each other all the time and thus get fake banners.
You created that ranking system, with the S, A, B, ... performance metrics. Why not utilize that along with honor reports to give people something that's more valuable? Potentially an IP bonus or a few Riot Points? I am sure there are other ideas to actually reward people in a meaningful way, share them!
Ultimately, if you want to create a positive community, foster positivity. Only punishing negativity isn't entirely useful. Haven't you heard of the compliment sandwich approach?