How do you know when you're using a SPA and when you're not? Seems to me, a well designed SPA is indistinguishable from a regular HTML site unless you're actively looking at the network tab. Could it be that you have a bad impression of SPAs, because you only really notice it when you're using a badly designed one?
Note that I've of course seen countless slow, bloated static pages - but that's pretty much never because of the tech stack - but because of bloated css, silly large images, and often horrible convoluted html.
Hn is of course a typical example of a web page that on paper would be great as an spa, but works fine as a static page with minor js (broken up/down links notwithstanding..).
D-lang forums is another :
https://forum.dlang.org/
Assuming a 64 kbps connection, and a 50%+ gzip compression, downloading a couple of pages of text is done in about half a second. If the user has such a terrible connection, they've hopefully turned off image loading. I don't think adding 40-400 kbs of gzipped js is going to help with the speed...
https://gist.github.com/Restuta/cda69e50a853aa64912d