The author critiques a ~50-year-old set of tech that has been developed piecemeal over those ~50 years to cope with a vast array of different goals and priorities. And proposes their own toy tech as a replacement, with apparently no sense of irony.
HTML was never designed for web apps, but it powers billions of them. CSS was never designed for complex dynamic UIs, but it does the job. If you seriously think "hmm, well this is shit, I can do better" then I invite you to take a seat and actually look at what this shit tech is doing, and maybe step down the arrogance a bit.
The problem is, as always with tech that survives a few years, backwards compatibility combined with mission creep. The author ponders HTML6 removing some redundant stuff. The problem is that you can't remove or change anything because doing that would break 348574793 websites and the people who rely on that stuff working exactly as it does now will complain. Meanwhile people are demanding that they can build 3D models using the same stuff that was originally designed to serve static written documents.
And, just while we're there, the answer to replacing the DOM is not to implement it in shiny new browsers. The browsers aren't the problem, or a route to change. You'd need to get every single website to change. Even the ones written by the company owner's nephew, who then moved country and doesn't talk to his uncle any more, so the website is a bit outdated but no-one knows how to fix it any more. There are approximately 3498573495645 of those.
HTML, CSS, JS, SVG, the DOM, WASM, all of that is miracle tech. Learn from it, study it as an exercise in longevity. Instead of complaining about CSS, learn why it was designed that way, why that particular set of ugly compromises came about. I promise that every single part [0] of all of this tech was debated for weeks by a large room full of very, very, smart people who came up with this solution because it was the only way forward at the time.
And mate, have some humility.
[0] OK, the original first version of HTML was probably not this, and was hammered together by Tim Berners-Lee, who probably never imagined that this would happen to it.