> Smart users will see TikTok doesn't really have a good recommendation engine, just good content, bite sized so lots can be produced.

This. Nobody has invented a Recommendation engines that really works, the ones that seem to work just have lots of content they can throw at you. I really think tiktok would be no less succesful with an engine that simply threw a random video at you. Recommendations is a really hard problem and anyone that solves it had essentially solved AGI