It's not even about speech necessarily, it's about what speech is amplified and what suppressed, and whether those perspectives are organic or manipulated. Also, who can read all the messages and analyse the trends.
If the US was as memetically robust as you say, foreign owned TikTok wouldn't be a problem. But even free speech cannot hold up under manipulation.
I think a lot of ppl in the US don't notice that this is the position that every other country is in with respect to US social media.