I would like to suggest some option to change the font size of headers in the Markdown editor. It might sound silly but the font size for the “#” header is way too big to my taste, and I wish that there was some way to change this.
(and yes, I know that I can edit the documents in another editor, which I often do - hello BBEdit, but sometimes it’s nice to do everything in DT)
Did you try Settings > Editing > Format > Markdown Font?
I set mine to 12. Paragraph text gets a bit small, but the headers are not too big. If I set it to 14, paragraph text is fine (to me) but headers get big. It is possible that selecting a different font may slightly change the relative sizes in ways that you might prefer.
Setting the individual header sizes would be nice, but I think the DT team has a lot on their plates.