Seems like it reflects a very subjective way that the author wants to implement web apps in.
I mean why should anybody invest so much time to learn alternative syntaxes and configurations to replace HTML, CSS, Javascript, module bundlers, existing SSR solutions etc, all at once??
Every new tech should have a convincing excuse to exist.
We've had the likes of HAML to simplify HTML, CoffeeScript to simplify JS, SASS to simplify CSS. These worked well as they optionally replaced a small part of the stack and took great care not to deviate too much from the underlying tech. They arguably had an acceptable cost/benefit ratio. The costs were little, as they should have been.
And for the stuff that completely introduced a new world such as ELM, Purescript, ClojureScript: ELM brought in established functional programming paradigms while at the same time providing a sensible framework for the common SPA. Purescript made the web accessible to Haskellers. ClojureScript targeted Lispers and made the Clojure ecosystem accessible to them in their web apps.
I don't see how I can justify the use of this "language" other than the fact that the author "likes it this way". Everything seems so arbitrary and the "all in one" approach seems daunting.
Every good developer goes through a "framework building phase" which is a very enjoyable and educative process even if the end product is mostly useless to anybody else other than the author. I think the author is going through theirs. Best of luck.