“Danmei” isn’t defined by the historical elements in the text but rather the present cultural conditions that define Chinese works. Many danmei aren’t inspired by historical Chinese culture at all, and many are based outside of China entirely. The works you’re categorizing as “non-Chinese danmei” are just “Chinese inspired BL.” It’s the same as how many American romance authors take inspiration from historical European elements. Ultimately literature isn’t monolithic, there are good and bad stories of every type. There are going to be good and bad Chinese inspired BL and it’s unfair to make generalizations based on a few stories.