Matchmaking balance
If you carefully studied Halo 3 ranked or competition game, you will notice that regardless of winning or losing, it's top two of either six man team that will ascend. That is pretty much balanced. In here, in this game, you still stick with giving negative lp to losers and positive to winners. That is what creates toxicity right there. That's what raised the stakes of ranked so much that everybody starts hating losing and start spamming chats when it's pretty much over early game. Much much harder for people to trust losers in their team, much much harder to keep that trust for next game. Abolish that system already. Assign points according to performance compared to the team. That is so easy! It's obvious that you are still using 'elo' system as mmr. And I am gonna repeat this: elo is designed for one player vs one player game. Not five vs five. Riot claims they like statistic. But statistic comparison or something should have clearly told them this long long long time ago that it's very inaccurate.
I promise you that if you change the system as I dictated, you will see enormous improvement in player behavior so players will continuously do their best even when they are losing so they may still get points. Four years of ranked and nobody thought of implementing this...