I would strongly disagree with the implication that The Great Wall is in any way racist.
The film is obviously fantasy, so why would it be racist to have characters from other races (than asian) to be included? This is not a historical film, so what "heritage" is being offended?
China has produced a number of movies combining Chinese and American (often white) stars. Forgotten Kingdom, the New Karate Kid, Dragon Blade, to name but a few. This is done to provide American audiences with a sense of familiarity. I don't think there's anything wrong with such an approach.
- All fiction is fantasy.
- It is not racist to have characters from other races.
- While having a character of the same race as the target audience for increased empathy may have the intended effect it is also condescending towards the target audience and would not be necessarily needed in a genuinely relatable story. This is also a variation of the "cater to the market" excuse to rationalize prejudice.
- A film does not need to be historical to be racist or offend a heritage.
None of the above is mutually exclusive with my point.
When any element of reality is used in fiction, especially the setting, that opens up the implication that other elements of that fiction are also reflective of reality or the reality-based elements regardless of whether that is true or intended.
There is also the context of a history and a pattern of racist "whitewashed" stories where white characters are the heroes saving the hapless people of other races, sometimes women when sexism is also thrown in, from themselves, their culture, their country, their men when sexism is also thrown in, or their enemies.
"The Great Wall" obviously uses China, Chinese people, and a Chinese landmark as setting. If the story fits into the above "whitewashed" story template then it is a racist movie which offends Chinese heritage.
That said, I have only seen the trailers for "The Great Wall" and the movie is not even out yet so I should reserve comment regarding whether it is racist until I have seen the movie. However the trailers don't bode well.