Most novels don't need anything more complex than a link to the next chapter at the end of the page. Maybe bold text, but a lot get by without. As such markdown will work for most. I've seen some novels with some really complex formatting, but those are rare (I read a lot of litRPG and still call them rare). However I mostly write technical documentation and I often hit limits of things markdown cannot do even though my documents are much shorter than a novel.