Notion and Markd.ly solve different problems. Notion is where a team plans, documents and tracks its work together, in shared pages and databases. Markd.ly is where you write a document of your own: a plain .md file on your own disk, written offline if you like, and exported on the desktop to Word, EPUB, LaTeX, slides, HTML or PDF. Keep the team wiki in Notion. Write the documents you own, and ship them, in Markd.ly, for $19.99 once on Mac, Windows, Linux, iPhone, iPad and Android.
The real question behind 'Notion alternative' is whether you need a workspace or a better place to write. If you need a workspace, look at other workspace tools; Markd.ly isn't one. If you want your writing as plain markdown files you own, Markd.ly is built for that.