reveal.js is mostly aimed at creating slides using HTML, it has markdown support for writing the content, but this project seems to aim to create the entire presentation from markdown. I'd compare it to deckset - https://www.deckset.com/
What's that advantage of using markdown? html is far more expansive in visual options.
Not Everything needs to be markdown.
Some things are just far less typing in markdown than in HTML, for example lists of bullet points and inline code.
Only “some” things?
...but then you're just using the wrong editor.
I largely prefer writing my slides in Markdown, for the same reason that I prefer writing (a first draft of) my letters in Markdown rather than in a word processor: this helps me focus on the content first, rather than the presentation.
YMMV
As a Deckset user, my only gripe (minor, and usually not a big deal) is not having an HTML version generated by it (this is why I wrote this CLI tool [1])