I don't think that's true at all. I mainly play Rocket League, and while you do have bad games, I'd say at least 80% of them are fun.
It does benefit from:
1. Limited coms (nobody seems to use voice chat, perhaps partly because it was completely broken for years), and while you can type, it's too fast paced to write much so mostly people just use quick chats sarcastically (What a save!)
2. Games are really short (about 7 minutes). You're not losing hours of your life if you get stuck with an arsehole.
3. People play a lot of games because they're so short, so the matchmaking is very accurate usually.
Trackmania (in all of it's online incarnations) seems to have mostly avoided toxicity.
But I think that's because you can't really impact other players. Everyone's racing their own lines, just sharing a chat room while doing so.
Matchmaking is a real problem in most games because of smurfing.
BAR has very sophisticated anti-smurfing, so many bans to out to people who thought they could trick the system.
You occasionally get smurfs in Rocket League but it's like 1 in 10 games so not a big issue IMO.