I'd be very interested to see some proper analysis of the difference in speed between HTML/CSS vs just JS, it seems obvious to me that the former would be much faster but then again I know how often "obvious" things are wrong.
Subsequently loaded-pages or resources can be significantly faster in webapps however, as they can request (or generate) exactly what they need.
The problem of slow initial loads is being addressed by tools like React by offering server-generated pages on the first load, and then transitioning to JS-based loading for subsequent loads. This offers the best of both worlds.
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https://codepen.io/anon/pen/weMwRz
Realistically, I'd probably never use it because it's so dependent on browser behavior, but still a cool alternative.