Nah, it's definitely Hextech, and I'll tell you why.
It takes forever to get reformed according to Riot's system. You can get a 10 game chat suspension and 3 months later still not be 'reformed' for it. And all it takes to get that chat suspension is a 4-man premade who wants to fuck you over. It's happened to me more times than I can count. Hell, I'm on the forums right now because I was afk for the first 3 minutes of the game (bathroom) and a 4-man premade got all toxic over that fact for the rest of the game and reported me for it. For 3 minutes. So now I need to wait a longass time before I can even queue. It's a broken system.
But that isn't the issue. Not at all. The system DOES have upsides. However, with Hextech, toxic players (or people who aren't reformed) aren't allowed to get rewards. Which really sucks, because as I said, it takes a really long time to reform. And not only that, but after every game you get a message saying "You are unable to receive rewards due to previous behavioural restrictions." or something along those lines. Which is kind of a smack in the face from Riot. Like, "Oh, you were toxic once? Well here, allow me to remind you after every single game."
In the forums after Hextech was added, there were posts all around with people saying that this was definitely not going to help them improve their behaviours, and they were absolutely right. The worst way to reform a toxic player is to slap them in the face with a fuck you, and that's exactly what Riot did.