I do appreciate them being upfront about not supporting rebasing, as it saves me the time I might have otherwise wasted in trying it out.
Fossil was designed to support the SQLite workflow. Git was designed to support the Linux Kernel workflow. Both systems seem amazingly well-suited for the projects for which they were designed.
Should you use Fossil or Git on your project? I suppose that depends a lot on whether your project workflow more closely matches the Linux Kernel or SQLite. There are other considerations, but I think that is the main differentiator of the two systems.
Side note: I've had a lot of help writing Fossil over the past 15 years, and especially a lot of help on the documentation. The article being discussed by this thread originated with me, but has been extensively edited by others with different ideas about the advantages and disadvantages of Fossil vs. Git. See https://fossil-scm.org/home/finfo/www/fossil-v-git.wiki?ubg for a complete timeline of changes to that one file, color-coded by committer. (BTW: Can Git or GitHub generate such a timeline?) My color is brown. If you scroll through the history, you can see that most of the edits to the article are by others. Which is fine. Just don't attribute everything you read there to me.