Indeed. A quick cashgrab shouldn't be expected to b some historically accurate masterpiece.
Besides, if you have a problem with Matt Damon playing a character in the Chinese army, here's an idea, how about you don't watch the movie?
I don't go out of my way to watch Tyler Perry put on a dress and play the same tired stereotype for the 10th time, because I'm not the audience he's selling to. Just like Wu just might not be the audience these people are going for. No need for whining, just skip watching it.