The risk here is China having the ability to sway and manipulate opinions of young minds in US over years by controlling what information they see on a daily basis. That is an extraordinary power which should not be underestimated.
The way it does this is to not show you more of what you have already seen, it is to identify what gets you worked up, and to exploit that by showing you progressively more and more extreme content. It highlights more provocative comments to you that are more likely to make you post an emotional response and engage in a long intense debate that causes more clicks and posts, and feeds more of your emotion back into 'the algorithm'. This is a dangerous spiral which can easily turn somebody who might have a weak opinion on something, into a mouth frothing raged keyboard warrior.
This is very powerful and dangerous, and it is purposely designed like this.
Allowing the Chinese government to have this power over young US minds? Thats what this is all about.
TikTok could be using blind algorithms as you hint at, but they could also bump content they wanted to.
I am convinced that if China put their best minds to it they could use TikTok to sway any election the way they wanted.
The data available to them about what reels swayed what people in what direction is immense.