It isn't less valid, it's different. There's no denying that people will face discrimination because of their region of origin, but the way such discrimination manifests is not perfectly identical to the discrimination POC will face overall.
There's also colorism, which is another issue.
With racism within Asian countries, you don't even need to go outside specific countries. Japan for example has treated the indigenous people of the country extremely poorly.
You are right that discussions about racism and prejudice shouldn't be limited to how it works in the US, but when talking about prejudice in the US specifically, bringing up different forms of prejudice that people face in other countries only dilutes the conversation.
Within communities such as ours discussions of such prejudice tend to only come about in response to specific conversations about prejudice. It's a form of Whataboutism. Taking an important issue and using it to shut down the conversation taking place.
Think about, we've seen things like this brought up before in discussions about diversity, but how many of those people have you seen asking for portrayals of discrimination based on region, without it originating in response to something about POC?
I'd be like if there was a discussion about police brutality and killings in the US, and there's a conversation going on where people are highly critical of the police. Then someone comes in and says the police are actually way better than how people have been characterizing them because, just look at the police from Iceland who killed someone for the first time in 2013. It doesn't really add to the conversation taking place.
While these things are important, they aren't always relevant to the conversations taking place.