Earlier quoted context omitted.
If you were writing this in 2019 I would agree with you. This perception is just already 3 years old now and so that social network has already gotten its additional audiences and many of those high schoolers (and their influencers) have grown up. There is a similarity of looking at Facebook in 2005 and looking at Facebook in 2008, and add in a much faster adoption cycle and infrastructure.
OTOH what happens to companies with teen users who grow up is that they lose their userbase and they die out along with other big influences of that current generation. You just don't have the time to stare at ticktock for 3 hours at 25 years old that you had at 15 years old, whether you are at the top or the bottom of the economic ladder. We see that trend in every social network.
I dont see a vine-like fate for tiktok
Bytedance is so much better positioned as well and already monetizing it