That's not 100% true. Amazon and (previously) ebay operate in china without problem but don't get a chance facing alibaba. Microsoft also do things fine. Uber was also there. The market that's really closed off are mostly limited to companies that don't support censorship.
Also speaking of world class, have you heard of DJI?
I did work for MS China for almost 10 years, and Microsoft does sell shrink wrap software in China, but they don't really do services there, they've tried and even though they are on the government's good side, it just never worked out for them. Microsoft is a good example of my claim.
Not trying to move the goalpost, but DJI is more of a hardware company, it isn't really an internet one. Any company that can operate outside of a services model will do just fine in China, since they are just shipping product for export.
How is MS a perfect example of your claim? It's proves even US company without much friction operating in China might not succeed. It had nothing to do with China closing off the market. Except the one really banned (google & fb etc), others just don't have a competitive product suitable for chinese market.
Also aren't we talking about tech company? Not internet company alone?
Or do you consider a market closed off if no foreign internet service company is doing well? In that standard US is also closed off because I can't think of a single successful non US internet company here.
China's internet market is closed off, not its hardware product one, so Intel still sells a lot of CPUs in China, while DJI sells plenty of drones outside of China and Xiaomi and Huawei even sell phones abroad like Apple can sell phones in China. If you count those as success and proof China is open, then that is definitely your prerogative.
But take the typical YC startup business models, most of those aren't going to be in those safe categories.
Also speaking of world class, have you heard of DJI?