Toxicity is reactionary
Want to address toxicity? Address the root problems that inspires someone to say something toxic. I would wager that the VAST majority of people punished for toxic behavior are not inherently toxic-- they have to be egged on in the first place. Those circumstances should not only be extenuating factors, but their causes should be the focus as a strategy to reduce toxicity.
Riot focuses on punishing sore losers-- it should instead focus on ungraceful victors.
For an example:
-Poor matchmaking -Intentional feeding -BM -Smurfs
Are my triggers. If you're a diamond playing silvers, and you flash your mastery after "outplaying" someone I WILL say something. Because you're a piece of human shit who happened to get lucky and is now taking advantage of an unfortunate situation to stroke your ego.