HN user
Both Orgzly-revived and Orgro support a lot more than a tiny subset of the Org format.
Do they support tangling of source code and export to all the formats that Emacs's Org-mode supports? Of course not. But they have all of what I expect for a knowledge-base on my phone, which is a lot more than Markdown was ever intended for.
an actual Emacs for mobile (actual emacs complete with elisp support, not the existing org mode apps)
There is an official fully graphical Emacs for Android (not just the terminal version in Termux).
that was a pleasure to use
Oh... Well, it will probably get better in time, as new features are added. For now, it actually works great with an Android tablet of 8" or more and a bluetooth keyboard. The small screen of a phone doesn't lend itself well to Emacs's interface.
Orgzly and Orgro can edit Org files on Android. (Orgro, also on iOS, along with other options.)
Both apps support Org-mode's scheduling, robust linking, and search features to some extent, features which don't exist at all in Markdown.
approximately nothing else supports it.
That's simply not true. There are numerous android and iOS apps that support it. There are implementations for Vim and other editors besides Emacs. GitHub supports it, for example.
I have not found a satisfactory (to me) solution for note-taking in Markdown that is open-source, plain-text, and mobile-friendly with local (non-cloud) sync. (Except for maybe Logseq, which appears to be moving in the direction of using a database.)
There are several such solutions for Org-mode.