I mostly use org-mode on a computer, with a screen and a keyboard. Markdown uses fewer characters for some things like code blocks (source blocks in org-mode), that is true. That said, not only does org replace Jupyter notebooks, LaTeX, and a dozen other things, it also has markup capabilities, which are simply lacking in Markdown (common mark if you want). For example checklists. Or citation. Or datetimes. Or spreadsheets. Or inclusion of other documents/files at a specifiable heading level. Or tagging of headings. Or marking headings "TODO", "DONE" and similar.
Many things in org-mode are modifiable. For example the "status" of a heading like "TODO", "DONE" and so on. You can add new words in document wide properties at the top of an org file.
I know there are markdown dialects, that partially cover this or that feature, but none to cover all that org provides out of the box.
The org format is much more suitable for any technical or scientific or academic document, that has any slightly raised requirements. In Markdown one often finds oneself using workarounds to make something look nice in the rendered output. Similar to how restructuredtext is powerful and can be used for academic paper writing and all that. Markdown is merely the lowest common denominator, too minimalistic for my taste. Good for a chat or messenger, but not really for good technical documents.
I still have to see a tool for writing markdown, that works as nicely as tooling for org-mode in Emacs, with all the things like changing heading levels for 1 heading or a whole subtree and export buffer or subtree, or cut visible or subtree, widen, narrow, folding, and all those nice things.