As with literally everything, it depends. Markdown is lovely for tech documentation, notes and journaling. It's simple and beautiful and mostly independent of layout.
Want to author something rich and expressive which has a modern web audience in front of it (either end user or editor) and it's probably not the right tool.
I work with large numbers of - let me call them "creative editors and authors". They want to embed video, pullquotes, tables, interactives. They want to float images, include audio and much more.
Markdown is not for them. Something block based and visual, namely Gutenberg or similar - is.
As ever (voice grows increasingly hoarse...) it's dependent on needs.