Without antitrust regulation, TikTok would have been sold to Meta, and that would be it. We'd have an even worse monopoly (which is not a good thing), but at least we wouldn't have this. With such regulations present, the US government both forced a sale and disallowed a sale to anybody who they didn't like, basically forcing TikTok to choose a government-approved partner. What did that partner do to become government approved? We'll never know.
Antitrust in the US (and GDPR in Europe) give regulators wide latitude over who to prosecute and for what. This makes it much easier to do under-the-table deals to achieve objectives that you can't or don't want to achieve by regulation, like restricting free speech.
Subjecting companies to such regulation was ok when it was about transporting cattle or selling bricks, but giving governments the ability to regulate companies that have a wide impact on speech, even if the regulations don't seem to have anything to do with speech, is just asking for trouble.