TeX [0] is in some sense "the one true layout system", but it's designed for printed documents, so it doesn't work on the web [1]. And in some ways, it's much simpler than CSS (you can build nearly everything from only a dozen typesetting primitives or so), but in other ways it's much more complex (since TeX is itself a fairly complex programming language). It's typesetting quality is still unbeaten by any of its competitors though, even 50 years after its first release.
[0]: https://en.wikipedia.org/wiki/TeX
[1]: But it does work on WEB :) [2]