I don't like user-generated video content so I rarely use YouTube and I've never touched TikTok. But I don't think algorithms really help. I really prefer the user selection here on hacker news.
People underestimate this. TikTok's algorithm makes the app enjoyable to use while most other algorithmic feeds make their respective service less enjoyable. I imagine that is because TikTok factors in other criteria beyond active engagement. At this point we all know it is easier to trigger active engagement through negative emotions. By simply prioritizing any engagement, algorithms like the ones used at Twitter and Facebook end up prioritizing content that delivers us those negative emotions in order to get us to engage. TikTok's algorithm also factors in passive engagement like the dwell time you mentioned. That ends up creating a more positive user experience because it actually learns what we like instead of just what makes us reply angrily.
I don’t know how much of figuring out what users want transfers from many short videos to text. For instance, dwell time seems an obvious metric but I find I ‘dwell’ longest on either things I find enjoyable or on things I find terribly boring. I hope it does transfer well – exposing people to more of the kind of writing they want seems generally good to me.