FWIW, I was hesitant about obsidian for the same reasons. I would've preferred an open source editor and a syntax like asciidoc. But the fact that everything is markdown and it being such a common standard does make obsidian being closed source more palatable[^1]. And tbh, for note-taking/"second brain" purposes, a relatively constrained format like markdown is pretty suitable. I wouldn't want it for technical writing but it serves the purpose for quick and dirty tasks like quickly jotting down notes[^2]. And any other markdown language wouldn't have the same amount of tooling (e.g. org-mode is underspecified and essentially emacs-only unless you see stick to a specific subset of features)

[^1]: see the creator's blog post: "File Over App" [^2]: in an ideal world a more sane/context-free syntax like Djot would have been nice