Building start-ups in China is great, if you're primarily interested in the China market. Chinese tech companies are overwhelmingly domestic capture entities, they can't get outside the country very easily.
The state now very openly controls all companies in China, directly or indirectly. They dictate what you can do, what you can build, what you can say, what you can sell, where you can sell, what you can do outside of the domestic market, how much capital you can move internationally, when you can move it, who can own your business, how much of your business foreigners can own, etc. You're not allowed to cross their edicts under any circumstances. If you fall out of favor for any reason, at any time, they will destroy you personally.
SV start-ups get the entire rest of the planet as a playground, almost entirely unencumbered by the type of highly restrictive state policies that Chinese tech companies constantly deal with. That's why Baidu was never able to go global and challenge Google. It's why China can never fully go global with most of their social products. They can never compete properly on the international stage with Google, Facebook, Instagram, Amazon, Reddit, Github, Snapchat, Twitter, Salesforce, Workday, Oracle, Windows, iOS, Android, MacOS and countless other types of companies and product categories. It's why WhatsApp & FB captured the world, and WeChat primarily owns China, but does not - and will never - own the rest of the world: aggressive state censorship sucks.
If I want to say that Xi looks like Winnie the Pooh, I can do that on WhatsApp. If I want to make jokes the Communist Party dislikes, I can do that on WhatsApp. If I want to mock Mao, I can do that on WhatsApp (or Reddit, or Twitter, etc). You can't do that in any ecosystem controlled by China (note, those are intentionally non-serious, illustrative examples, China's restrictions are far more smothering and comprehensive).
SV can't get into China. China mostly can't get outside of China. SV wins.