I like that zim is not automatically a hosted solution but a local app. I would love to see more local apps for archiving solutions and PKM. I just have some issues with the Zim app itself. It works nice for some of my use cases, but not for all. And I wish it would just use markdown (I know it has limits). Stuff like that.
I think Zim does not really fit into the discussion because it does not rely on easily exchangeable standard software like a file explorer and browsers.
That said, I believe that notetaking applications mostly exist because file explorers do an extremely bad job and integrating applications with them is too limited or at least too reunified. Look at what these applications offer. 80% of it is actually the task of a file explorer.
Zim is very much based on the file system. Each note is a text file and if it has attachments or embedded images they go into a folder named after that text note.
Whilst not in markdown the markup used is easy to understand and convert. Zim itself allows you to copy a note to the clipboard in pandoc markdown and export the note to markdown and/or html (though admittedly the styling for html it atrocious).
I am not against zim or obsidian. In fact, I currently use plain markdown wit vs code, which boils down to a similar situation. But vs code and its extensions may be gone in a while and then I will have to look what to do.