The point of a js web app is that you can run it in a web browser. Hammers and nails are even older than server side rendering, yet somehow they still function perfectly.
Hammers and nails equivalent is cgi/perl/php/asp and they still do a fine job. You can use the screw machine to manually punch down screws, but then why not use the hammer and nails instead, as you do not see the advantage of the screw machine.
Not really any different from building say a PHP app that serves an API to a mobile app.