This is why we added http cache headers, CDNs and caching of common assets, and cross domain requests. All of which are being assaulted for various levels of "privacy" concerns. Privacy I never asked for mind you, but I get it anyways. Though how convenient that tracking still happens, I still get ads, my content still doesn't belong to me, sites are slower, everything is an App, and the general experience and openness of the web is Down.
I exaggerate a bit to prove a point but the gist is definitely happening, we're just waking up to it slowly.
I mean, there's a reason ajax took off in the first place. Member having to reload the entire page on every user interaction? Member iframes? Member flash and silver light and java applets?
With stuff like web sockets/Web rtc /whatever new awesome sauce is out today a lot of that has changed, but that's still really the same spirit of ajax anyway, just with actual persistent connections instead of hacking it with long polling.
You can write a shitty system regardless of paradigms used.
You can write a beautiful system even with painful primitives.
All it comes down to is how much time and talent you're willing to invest, which is admittedly a cliche and non answer, but true nonetheless.
AJAX took off because it's good for interactivity. If your "AJAX" requests are literally blocking the functionality of the website then they're no better than returning a big HTML blob. Your page just takes longer to load and the user experience is worse.
Returning new HTML blobs will never be faster than an equivalent AJAX roundtrip. In other words, if AJAX is slow when "literally blocking", fetching new HTML is at least that slow as well.
Static HTML only has a potential latency benefit on first load due to the ability to save render-blocking resource roundtrips. For later requests where those resources are already fetched, it only adds bandwidth overhead.
But that cannot help with interactive pages or web applications, and in other cases it can be a bandwidth/latency tradeoff.
High latency is always bad and should be avoided. Serving content from the served contentinent is the minimum requirement for good UX.