I appreciate Valve for having both an in-game skill score as well as a behavior score. Once your behavior is maxed out chat becomes an entirely different experience.
Is that simply cultural? DOTA is well over a decade old. If everyone's toxic and behavior is self-moderated, then toxic behavior is not just normalized but reinforced.
And as someone with that many hours too... Go check a 8k behavior score or below. The system is working. It's just that the depths of hell are deeper than people think.
It could be more aggressive at lowering score tho, true. Used to be. They "buffed" the gain per 20 matches last December, but it was great before (And even lowered the scores of streamers that had it coming).
Here's a chat log from a game I played yesterday: https://www.dotabuff.com/matches/7902208511/chat
Some wholesome banter and that's about it.