I think you made some fair points...but you did exaggerate one point, imo.
Imo, Youtube ain't dying because of TikTok. It's core audience of millennial and older aren't expiring yet. I'm still waiting for LittleKuriboh to finish Yu-gi-oh the Abridged Series.

There is also no substitute for "involved and substantial" content like tutorials, entertainment....basically more coherent videos, which TikTok isn't even trying to replace.
He did want you to present some more solid evidence. I do think anecdotal evidence can be accepted up to a point. Sometimes, a poll questionnaire does not capture the "flow of actions" that personal observation does.
I mean, this following article about TikTok being used as a search engine could have helped your point. If TikTok is being used as a search engine, that's a threat to Google's foundation
https://www.nytimes.com/2022/09/16/technology/gen-z-tiktok-search-engine.html