I mean, this is why I think PDFKit is a good comparison. Could you render your app's entire UI as a series of PDFs? Absolutely! Should you do that? Uh, probably not. You should use the native controls Apple gives you for buttons and dialogs and input fields and so on.
But WebKit is the native UI for HTML, and Markdown is intended to be transpiled to HTML.
It's irrelevant what Markdown was meant to be transpiled to. When people say "Markdown support" these days, they mean "rich text support", since Markdown is actually just ASCII. It is ridiculous to need a Web renderer to render rich text, on any platform. Even terminal emulators can do it.
That’s how it originally worked, but Apple has moved away from PDF to other native GPU frameworks for drawing. Now window content is stored as bitmaps instead of redrawing vector instructions.
You’re correct. I meant to say textures, but even that isn’t completely accurate.
AppKit used to generate the bitmap directly through CoreGraphics (PDF model). Now it uses Core Animation and Metal and no longer draws the bitmap directly.
But WebKit is the native UI for HTML, and Markdown is intended to be transpiled to HTML.