Why does it matter if Riven is fine in some regions?

Why is it worth dividing by region to determine if a champion is OP? Why doesn't a simple average weighted by number of games make more sense? You don't want to hurt one region to make another better? If that's the case then wouldn't you go by the same logic of the skill tier divisions, i.e. "If it's OP in one tier/region, then it needs to be nerfed to fix the experience of players in that tier/region of play."

Riot's argument seems to be "By that logic we should nerf Jinx because she's destroying in Vietnam," to which I'm thinking "Oh yeah, that sounds like a good idea, it must suck to play in Vietnam and have her tearing up games."

To me the only two methods that make sense are "Don't divide stats by region, try to estimate the champion's overall power level based on an average," or "Split the stats by region and consider where the champion looks most broken because that's where it sucks to be a League of Legends player." Maybe it's worth considering, "Stats of different regions need to be adjusted based on the average skill level on that server," which could be estimated based either on examining champion grade statistics or occasional case studies in cross-region play, but that sounds like an option for down the road if that information isn't yet available.

She doesn't even seem that fine across other regions: if you give each server equal weight she seems OP in over 50% of them, and it's especially weird to see it referred to as a "western phenomenon" when those servers include JP, OCE, BR, and LAS.