I've been copy-pasting markdown to/from the note editor on Android.
Are you looking for an import from file button? Import from multiple files?
It is more difficult to copy-paste the contents of a markdown file on Android (I've been using Termux to do this...), so an "import from markdown" would make sense.
Additionally, (at least in iOS) sharing a .md file with Joplin attaches it to a new note. It might make sense to create a new note from the markdown file instead.
Why is it a headache? How can you function between devices without sync? When my android apps start, they check for updates and sync. I don't do anything. Well, honestly, I look, and see it says syncing and has a cancel option, which I don't press. Not pressing cancel, doesn't seem like a headache. I've synced in a couple of seconds, faster than it would take to import copy a file somewhere then find it for importing.
Because if you do not want to pay the Joplin subscription, or you don’t want to use any of the options available (Dropbox, etc.) to sync, then you’re screwed. Plus, I’d like to use Google Drive, and this isn’t supported yet. So, yes it is a headache, and an import from file button would just make a lot of sense.