Well, with a SPA, 0% of your website may be rendered on the server just like your other clients. That's basically the defining feature, though of course they can be rendered on the server as an optimization detail. They even still use AJAX, so I didn't quite understand that bit.

I'm not sure what you meant with the rest of your post. There are technical upsides to having zero web client presentation logic implemented on the server at all. But it's just trade-offs.

Maybe you're suggesting with your "grunt work" comment that most complexity for most applications lives in the UI rather than the API? I'd agree. It's why there are upsides to keeping UI implementation off the server.

I just like to avoid the HN cargo cults of "this = good, that = bad" and "the people who do $X are probably incompetent."