First, about my own background (and therefore qualification to answer this question): I'm a member of the Chinese diaspora, and fluent in the language. I've visited China many times, but I don't have direct experience with academia in China. However, I have had plenty of contact with Chinese colleagues (PhD students/postdocs), many of whom either plan to return to or have already returned to China.
Living in China can be difficult, but not for the reasons you think.
Any concerns relating to lack of freedom of speech/government oppression/censorship are wildly overblown. Unless your hobby is organizing large protests, life in China is just like life in any other country. You work, eat, sleep, play. You can think and say whatever you want and practice whatever religion you want. You won't be voting in local elections, but then again, this applies to living in any foreign country.
The Chinese government has its flaws, and there is certainly authoritarianism in China. But for 99.9% of middle class citizens and white collar expats (such as researchers) the presence of the “authoritarian” government has no practical effect on day-to-day life.
In addition, I find the OP's story with his Chinese classmates to be highly unusual. Of the Chinese people that I have encountered working in academia in the west, most wanted to return to China eventually (whether due to job opportunities, or to be closer to their family, or because they actually find the quality of life (i.e. food, infrastructure, public safety) to be better in China than in the west), and of those who preferred to stay in the west, for not a single one was it due to political reasons or "lack of freedom".
The real challenge is simply living in a foreign country with a different language, different culture, and different systems for everything. And realize that "foreign" is relative—to a western person, east Asia will be far more foreign than another western country. The level of English proficiency among the population (even among educated people) is quite low, and if you can't read the script, you won't even be able to read signs in the street. The culture shock can be huge. The answers to this academia.se question are a good resource.
In addition, moving to China comes with its own extra difficulties, since in many ways China is like a separate universe. If you go to Japan, for example, you'll experience the same level of culture shock, but at least you can pay with your credit cards/get money from an ATM, and use a lot of the same apps and websites (Google maps, etc.). Not in China. In China there is a different Chinese equivalent of everything that you are used to in the west. The great firewall is not a problem, as it is easily bypassed with a VPN (anyone who says that using a VPN is banned is misinformed). But even if you can access it, Google maps is basically useless in China, for example. Setting up payment systems is another headache, as most places don't even accept cash, so you need wechat or alipay, but first you need a Chinese phone number and bank account to register for those apps. It can often feel like one is in a chicken-and-egg situation.
Finally, something else that was a problem until recently, is the fact that China was a developing country with all the usual developing-country-problems (pollution, filthy public toilets, food safety, poor infrastructure, etc.) This is not much of a problem anymore, as in most first-tier cities in China today, the infrastructure, cleanliness, and general quality of life are on par with developed countries (except for the undrinkable tap water).
