Rioters have inflated ladder MMR

They are guaranteed to not get any trolls or toxic teammates because they have the power to instaban people instead of just powerlessly threatening reports.

This is a huge advantage especially plat where id say ~50% of games, if played out would have led to different results. Instead our jungler failed a gank top and now our top is afk. Or the score is 12-17 at 20 mins and doesnt look pretty so we have to surrender, etc.