With modern Usenet there are about 8 or so backbones used for file sharing. Your Usenet provider/server would connect to one or more of these backbones.
Its true Usenet is designed for federation, and in the 80s and 90s it was thousands of servers but today commercial Usenet providers just resell these 8 backbones.
I’m aware. You may have missed that I made that distinction in my first sentence.