I have no doubt that China can and does buy data from data brokers. I think it's unlikely, however that any of the major players are going to be willing to sell all their data on anyone- being able to target ads to individuals is their entire value proposition after all. On top of that, Facebook, Twitter, and Instagram have fallen pretty heavily out of favor with folks in their teens/early 20s (i.e. the demographic most ripe to be sources of bad OPSEC).

But even assuming that an adversary could buy all the data they could possibly want, doing so could tip off anyone who cared to be watching about the sorts of data they're interested in. This is generally not something you want as it can reveal your own strategic concerns/intentions.

Having your own app that can collect whatever you want, where you can promote whatever information/view that you want is a pretty big advantage over buying data.

If the argument is about privacy, I think banning tik tok is complete bullshit. If it's about limiting intelligence gathering and influence campaigns, I think it makes more sense.