If i made my own RNN to detect toxicity and positivity, would it convince riot to do it themselves ?

If it was reliable, accurate, and consistent it would at least undoubtedly be a fantastic resume piece. I don't believe any of us here can speak for whether or not it would cause Riot to do anything though, especially as we don't know what they've tried or developed internally.

The verbal detection system is already 99.9% accurate. So you have a tough hurdle to overcome if you want Riot to adopt your verbal detection system.

Gameplay behavior is a different matter. ANY company would pay good money to buy a good gameplay detection system. That or they may hire you.

That said, what are you trying to combat? Verbal toxicity? Gameplay toxicity? Something else entirely?

Doubt it, but who knows.