Xi is a bad actor. He actively removes opponents, like his predecessor, Hu Jintao, who sat right fucking next to him and was publicly removed.

This is a bad conspiracy theory. Hu Jintao was allowed to sit at the table because he is an important historical figure. He's in his 80s and has Alzheimer's. He was having an episode at the table and was escorted out. The idea that he was publicly removed from building and disappeared is tabloid-level misinformation.

Under Xi, China is asserting ownership of international waters in the South China Sea that have historically been either international waters or even owned by smaller nations.

Nations fight over territorial waters all the time, whether it's Turkey or Kenya or China. There are EEZ disputes in the North Sea between Norway, Denmark, Iceland, and the UK. Why should I care whether China or the Philippines own the Spratly Islands? What does it have to do with China being Marxist or not? I really don't understand why you even brought it up.

Under Xi, the Uyghers' and Mongolians' culture is actively being erased by outlawing local religious and cultural customs.

Neither their local religion nor cultural customs are being infringed upon. If anything, the re-education programs in Xinjiang seek to remove recent (90s-now) religious influence from Arabian missionaries, who have spread Modernist interpretations of Islam that are what is endangering local Traditionalist Islam in Xinjiang.

The one thing I would actually agree is an issue is language - the biggest sticking point in Mongolia is that recently public schools have been mandated to teach in Mandarin. However, nothing is being done to prevent locals from speaking Mongolian at home; the goal is just to guarantee that all people in China are fluent in Chinese, while a Mongolian-language school system means some amount of people are just never learning Chinese. Cultural assimilation isn't even really the goal; not knowing Chinese is correlated with worse career prospects for indigenous people in China.

And of course, most countries in the world, including the U.S., mandate that public schools teach in the official language. This is nothing new nor unique to China.

There is a similar problem in Tibet, where in addition to the above issues, boarding schools are being mandated for rural children because it's less expensive to have a large, centrally located boarding school in low-density areas than managing a public school in every remote Tibetan village (China recently outlawed private schools, which I think is a big plus for equality of opportunity).