The reason it took more than a year for me to realize this phenomenon is because when I first visited the country then I relied on travel agencies, international hotel booking apps, and had accommodation provided for me. It's certainly possible to live in China for even a decade without realizing the reality of the situation if you exclusively stay at 4-5 star hotels, or only book hotels through international hotel booking apps, or rely on agencies to help you find apartment and other type of accommodation since they have a list of the ones that accept foreigners.
https://www.ceicdata.com/en/china/starrated-hotel-operation/... claim there are 10 million hotels in China - what percentage do you reckon are included in the international hotel booking apps? My guess would be less than 0.5%. That's why you need to walk into the random hotels/apartments you see on the street if you want to verify the reality of the situation. For you specifically then it might be difficult since you're ethnically Chinese, so while you might encounter some discrimination and exclusion from society (if you don't have a national id card) then it certainly won't be comparable to what white and especially black people experience while living in China. In my experience then the 9/10 number is not an exaggeration at all but if you asked other westerners who visited China then they will likely give different numbers based on their price range, location, booking method, etc.
I also think you greatly exaggerate how much you actually learn about another country by going there for a short trip. Even the most brutal regimes can look like a wonderful paradise, e.g. see the national day celebration in 1959 which took place at a time where tens of millions of people were dying of starvation (https://youtu.be/M-XQSffVpfY?t=43).