Really? This is what you're upset about? Limiting culture to a race is racist in itself, white people living in Asian countries typically follow the sentiment of "when in Rome do as the Romans do" because the native population doesn't care like Asian Americans do, in fact they may even take it as a compliment. When random people off the sidewalks of Tokyo were asked about their feelings on a Scarlett Johansson playing the lead role in Ghost in the Shell, most of them were openly excited about it and the rest said they weren't bothered in the slightest. I know caucasian men and women who met, married and settled down with their spouses in Japan and wear kimono to special occasions with them and all they get are compliments. Do you know why this is? It's because culture is an abstraction that is meant to be adopted by anyone who chooses to live in its midst, it's not meant to be limited to one skin color, or one set of facial or bone-structure features.
I doubt this was Riot's intention, because I doubt they even thought or cared about race when they created the characters if it even occurred to them at all. But if anything they're not missing an opportunity to create more diverse characters; they're seizing the chance, by tearing down the racial walls and barriers that people keep trying to build up around cultures they pretend to protect from getting "whitewashed." So what if Ionia is inspired by Asian culture? Are you saying that because someone's creation, their baby is inspired by a real-life culture or group that the characters who hail from it have to look like those people as well? Let me tell you something about ideas and values: nether genius nor idiocy is confined to a single appearance, ethnicity, or class. Anyone can be stupid, and anyone can be a genius.