The fact that Remender is a white, American man is the key factor. The ethnicity of the characters is irrelevant.
When he has Famine (?), the geisha, talk in Uncanny Xforce about how a woman should be, that was just perpetuating the stereotypes that many Westerners believe about Japanese women.
I don't know if anyone else in ComicsGAF lives in Japan, but of course I'm going to be more sensitive to these things than other readers. The behavior I witness in Japan from Western tourists, especially regarding Japanese girls and women, is utterly disgusting. Sexualizing Japanese women and presenting Japan as nothing much more than land of samurai swords, geisha, ninja, honor, and shame is lazy. He is not even close to the only person in American comics doing this, but he happens to use Japan a lot, so that's why I target him. I actually love Uncanny X-Force and Deadly Class... although I'm pretty anxious about reading the issue going into Saya's background. Yikes.
Anyone I've talked to that actually understands Japanese culture has brought up that same criticism without me even mentioning it. Perhaps this just bothers Asians more than others, but that makes sense, as cultural appropriation of Asian cultures is pretty prevalent in America. It feels like Remender learned everything he knows about Japan from anime or something.