You could do the same thing with a Markdown file, but I wouldn't call it simpler than Org. Maybe by simple you meant "familiar to more people"?

I meant 'less markup' (in the sense of a simple ratio of markup characters over total characters). Now you can say that the markup is still fairly low and actually useful. But that goes to my second point of why not just use HTML. This is pretty much exactly what it's been designed for originally.