Yeah because they're taking a prominent/important role away from an Asian actor (when there are so few opportunities for them in these types of films to begin with) and giving it to a White person.
And that's the difference between this an Mordo. You make a White character black and, there are still thousands of White comic characters out there. You make a minority one White, well there aren't nearly as many non-White characters to begin with, so it has more of an effect.
And again, they then shot themselves in the foot by essentially making her look like a "stereotypical" Asian monk/martial arts master anyway. Robes, shaved head, living in a temple/monastery, etc it's all there. They just made her White. This contradiction is pretty much the worst way that they could have gone with imo.
And the whole "oh they should cast based on talent" sounds like an excuse to me. Guess what, there are likely some really talented Chinese actresses out there that they could have cast.
And finally, when you have a movie that seems like it's spending a lot of time in Asia, has a lot of Asian philosophy/mysticism/aesthetics/etc, and is keeping a big chunk of Strange's traditional origin story seemingly, but the only main cast member who seems to be Asian is the freaking manservant, that's a problem for many people. And they're not wrong for thinking that, because it does stick out.
I agree, the aesthetics aspect is the worst thing. If a character is changed it should look completely different to the stereotype they're trying to avoid.
Most people wouldn't have cared if she'd just looked like how she did as an ancient vampire in Only Lovers Left Alive. (Look at Edge of Tomorrow, based on a Japanese story but nobody cared)
Another problem though is if it ends up like the comics and The Ancient One is killed off to further Strange's character development, that wouldn't have been a good role for an Asian person either.