This was exactly the kind of answer I was looking for when I asked my question, so thanks again!
HTML was never intended to separate data and presentation. That's what PHP and other server-side languages (ColdFusion, Perl, etc) were used for, because HTML specifically is a presentation. Moreover, DOM, as HTML representation, is also a presentation. Considering high availability of network bandwidth, I'd say there's no more need to squeeze data into client-server channel, that's where server-side rendering comes into play with thin client just doing presentation thing.
Today, we see a mish-mash of HTML + CSS (+JS) being used for presentation, since neither HTML, nor CSS can successfully solve every problem on their own. They often also need to rely on JS.
Regarding bandwidth and SSR, I disagree also. I think we should do things more efficiently where possible, not less. In my current SaaS product, if we were doing SSR instead of client side rendering, our hosting costs would be through the roof right now. As it stands, we have one large-ish download at the start, followed by very small JSON payloads thereafter. Plus, using service workers, it can work offline, which is not really possible with SSR.
>In my current SaaS product, if we were doing SSR instead of client side rendering, our hosting costs would be through the roof right now
It's good you mentioned your product instead of generalizing implicitly. Because SSR in some cases allows you to prerender pages and host them statically, thus significantly reducing server CPU and RAM load, and also making page loading time very fast.
>Plus, using service workers, it can work offline, which is not really possible with SSR
Similar scenario is possible with SSR, allowing for completely offline operation. SSR implementations usually require scripts to be run on the client side, and also allow for defining explicitly server-side-only and client-side-only scripts, including full transition into kind of SPA for specific pages, as well as a full SSR prerendering with dead-static content on both server and client. And gzip can help to reduce the bandwidth required.