So his central thesis is that JS has been getting all of the love while HTML and CSS have been marginalized. I want to empathize with him because he's a seasoned vet in programming and has been at it longer than I have. But, I've been doing web development since i was 12 on pet projects, and we totally have been making great strides in web UI.
If you made a website in the 90s or early noughts, everything was tables. Do you remember how to make a button with a bevel in 2005? You made a 3x3 table, and had to splice an image into 9 different sub images, and then stitch them all together. Now you have background:linear-gradient and border-radius. I mean, maybe you take this for granted now, but seriously, that was game changing for me when those things came out.
Now add on UI frameworks like Bootstrap and Zurb. Before everything was a JPG photoshop mockup. Every design was treated in isolation. There were entire businesses revolved around taking a PSD and turning it into HTML/CSS. Now everything is a component. It's reusable...and useable. Sure, we may have watered down design to the point where largely every SaaS landing page is the same, but the speed with which we can get developers to convey trust via design is vastly improved over the old days.
Sure, JS frameworks are all the rage right now. But we have made serious strides in web UIs as well.
Has ui improved? Yes. But is ui a good experience? No.
Simple tasks like centering or multiple equal height columns are now possible (yay!) but aren't actually simple.
A large majority of css techniques are trying to get around how css tries to work.
Flexbox is great compared to what came before...but have you tried teaching it to someone new? Zindex and stack context? Style a container based on what it contains?
Compared to the improvements in js, and compared to the ease of use of non web ui building, there is a lot of room for progress.
I'd be genuinely interested in hearing about your experiences with other layout and styling languages or tools, and what you like about them. I used to hate on CSS a lot, but eventually changed my view and grew to like it, and I think given its history it's actually quite good. I haven't had much in-depth experience with native alternatives, but when I've tried em out I usually found they each have their own shortcomings. For example, on macOS I'd say Auto Layout is certainly easier when getting started, but as soon as you want to create your own components from scratch it becomes rather challenging.
As for styling a container based on what it contains, if you know of any examples which showcase good execution of this idea I'd also love to check em out. I know of at least two proposals / libraries which are attempts at tackling that problem in CSS; take a look at CSS-Element-Queries [2] and EQCSS [3].
[0] https://gist.github.com/cesarandreu/3e87cb6993bedeb162b56482...
[1] https://github.com/facebook/yoga