Wait what? Single digit ownership of a billion dollar company gives you a lot of access and control. Especially if it's something that the other 90% don't care about, but you do (eg. chinese politics).

No. It doesn’t. Unless they got a board seat as well.

I love the idea of a group of uniformed Chinese generals showing up at the annual shareholder meeting to demand Reddit do... wait what does the CCP want Reddit to do?

If they do, they're not very good at exercising that control. There is plenty of heavy (and heavily upvoted) criticism of the CCP all over Reddit.

Seemingly "small" investments were enough to strong-arm the NBA and Blizzard into punishing people speaking out for Hong Kong, so it appears it gives them enough.

It has nothing to do with their investment. It was because nbas market share in China is huge. I think you are upset with the NBA here, they chose profits over geopolitics.

What's the leverage?

Naively I would assume that the worst would be that when such a small investor sells his shares then everybody else has an opportunity to make a cheap offer.

What investment is being referred to here for the NBA? The NBA including individual players all defended China. Money being the reason.