But China already bans tons of American services from Google to Twitter, no? And otherwise makes the regulatory burden so incredibly onerous it's very difficult to operate (e.g. LinkedIn) for some tech companies when they want to build up domestic champions

There's no hysteria here, and surprise, most nation's act out of self-preservation or with interests of their citizens, or what you call nationalism.

> If data harvesting was a genuine concern ...

It is, and that is what is going on here, with TikTok the beginning. EU is also helping here, so kudos to them. Hopefully Discord next.

>China banning American services is to the detriment of Chinese users and competition in China, there's no reason to emulate censorship.

This is not true. China financializes everything, and pumps capital into projects at rates unseen and unmatched in the history of the world. There is plenty of competition, as evidenced by the fact that China has apps that are fare more efficient and feature rich than anything in the US. See: WeChat.

Good luck winning a war if you're not censoring your enemy's propaganda.