Yep. Here's one example.
This writer joined Medium about a year ago: https://medium.com/@allmylittlewords
She's historically been a music writer, but came to Medium writing all sorts of things.
Earlier this year, she wrote a story that got a lot of traction:
Based on the success of that story, she decided to start a new publication, serving a very specific niche that no other publications on Medium were focused on: https://medium.com/pink-hair-pronouns
The publication is now in the Boost Nomination Pilot and she is promoting the work of other new and unknown writers on the platform.
This is just one example of many stories of how folks can carve out their own niche on Medium. I'm not saying it's easy or works out for everyone, but I see folks carving out content niches every day on Medium.