As Rails + Turbolinks has shown, unsurprisingly, users don't care what renders your page. As you said, they just want it fast.

Server side rendering HTML and serving it up works perfectly fast for pretty much every site which is read only content or forms. The of 3rd party scripts running on every page are the issue.

Also as a major negative against SPAs, once a script is loaded - it's going to be ever present on every page afterwards - enjoy explaining why payment details page needs 20 3rd part scripts running on it. Not possible to unload scripts.