Isn't TikTok just videos though (I don't use it so I'm guessing)?

It doesn't really seem useful for sharing the same kind of information that people use Facebook for (mostly text based information, questions, etc).

You'll be surprised. People post videos with walls of text or post a video of them narrating whatever they were planning to write.

For now yes, but I would say it's really meant as replacement for Instagram rather than Facebook. So videos only seems fine compared to a service that was primarily for pictures.

They can always expand, but I feel like these social media services usually have a hard time pivoting to a different medium after their initial success.

TikTok feels like YouTube. It has hundreds of millions of users, but only a small fraction will ever post anything. Unless the dynamics of TikTok radically change, I can’t see it being an Instagram replacement.