markdeck can create diagrams and charts on-the-fly (graphviz, ditaa, plantuml, a2s, Vega-lite). And it can export the slides as PDF or as standalone HTML file. Plus out-of-the-box auto-reloading the slides on change, emojis, font-awesome, math-jax, and some other stuff helpful when authoring slides...

But when you don't need any of the above, then markdeck in fact has no advantage over plain reveal.js and markdown.