You can have your cake and eat it too. Use progressive enhancement/graceful degradation so that users with JS get immediate visual feedback, and just fall back to reloads without JS.
That's more work and more messy than just writing the whole thing as a SPA from the beginning IME. I'm talking about real interactive applications, not simple blogs.
Precisely. That's exactly what you get by disabling javascript on most sites.
Two of the fastest sites that I know are sourcehut and the D-language forums. They are much snappier than any javascript-infested site.