Suggestion: Copy League of Legends honor system
So many threads here are bringing up how terrible this leaver penalty is, and if you remember in S2, many threads brought up how terrible the leaving-situation was. So maybe the whole punishing-approach isnt the right way to go. Maybe instead of punishing wanted behavior, why not reward good behavior? This is exactly what they did in League of legend and the decrease in toxicity particularity between teammates is really noticeable.
The "light-version" of this could be rewards in form of loot boxes, unique "good karma"-skins or banners etc. Priority to new game modes that arent yet available for the public could also be a reward. But if you want to give it some real impact, then make it so matchmaking is affected by each players honor, that is, make it so the rage-quitting, toxic aholes get matched in the same team where they can rage quit, curse and spam pings at each other as much as they want.
I think you underestimate how much more effective positive reinforcement is compared to punishments.