There is a fundamental difference in consuming short form content, and reading a book- no matter how trashy the book is.
When reading for long hours, or for a short time over days and weeks- it teaches you to concentrate, to have some kind of discipline. It helps you focus and develop empathy. Reading is fundamentally different for the reader, and it makes them do other things well. Reading trash trains you to graduate to serious books- this is true for many.
But consuming TikTok readies you for more TikTok. More Shorts and Reels and Snaps. Wathing short form stuff damages one's ability to do other things as well.
And from the creators' perspective, I think trying to keep up with short form media for engagement's sake actually impedes their ability to create more serious stuff.
I don't totally miss his point, though. When smartphones and "internet places" spread as media, those already ready for serious stuff will graduate to those. And yes, these places will have a small role to play.
But they are definitely more negative than positive.