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.

Azure Cloud is operating fine in China, so does Office365. Are these services?

Also AWS China is a huge deal.

You mean the one run by the Shanghai water company?