This is like suggesting cars' days are numbered because skateboards have become extremely popular. Sure they technically are competitors in some extremely narrow ways, but suggesting so belies a misunderstanding of the underlying uses of each.
Tiktok is not a competitor to YouTube. Long form vs short form. It's like comparing tweetes to long form articles. I've actually seen Tiktoks promote YouTube videos.
[0]https://www.theverge.com/2021/9/7/22660516/tiktok-average-wa...