As someone whose been playing regularly for the past 4 years, 2-2-2 role lock was by far the biggest reduction in toxicity. It removed an entire class of bad communication like “switch off DPS” as well as the stress of convincing 5 strangers to use a particular comp at the beginning of the game. Before role lock it seemed like every single game was a freaking argument.

They also released player reporting and endorsements though it’s harder to say what the overall impact of those are.