We need to find another term for this (Server Side Rendering = SSR). SSR is starting Firefox on a server with X-forwarding or something. How is producing a complete HTML document on the server = rendering? Then PHP has been rendering webpages for years.

Offloading the actual rendering-engine from gluing together the HTML document from parts fetched or produced by Javascript prior to actually rendering the webpage can probably be a good idea in some instances. But this is hardly a new technique. Using Javascript to do it doesn't make it something different than PHP or the good old CGI scripts in Perl/Python.