I think Markdown is a good argument for potentially being
too simple. It's good for what it's meant for, but it stumbles for stuff like blog authoring.
I am somewhat happy with AsciiDoctor[0], although I honestly feel like AsciiDoctor goes farther in the other direction than it needs to and ends up overcomplicating itself. I spend more time reading the AsciiDoctor documentation than I want to.
Would you be willing to expand more on what you mean about a separation of concerns vs a simplicity of concerns? I was using the term in the sense that Markdown not only doesn't embed logic, it also doesn't embed style. It's literally just content, and you use other technologies to get at the other parts.
In contrast, LaTeX embeds logic, style, and content. When I work with Markdown I don't stop thinking about style -- I just use other tools for that. That separation allows me to then give other people content access without asking them to worry about CSS.
I guess I could see that it's a flat-out dropping of meta-programming from my document generation (although Markdown is a very easy compilation target for templates). But that just kind of gets back to my original point -- do you really need to meta-program blog posts and books, given that it greatly increases the complexity of LaTeX? Would it be better to have a simpler version of LaTeX that got rid of that functionality and said, "I'm just gonna do text layout really well, and nothing else"?
[0]: https://asciidoctor.org/