Web extensions are extremely limited by Apple. That is why we don’t have uBlock origin. A PWA alone would not get the job done. This isn’t talking to an API. You would have to parse out the HTML and reformat it, intercepting links, etc. View the source of new reddit and you will see what I mean.
You also can’t design around old reddit because they are killing that next.
It’s possible to write a web app that accesses Reddit APIs and loads comments and gives you an Apollo-style experience. You seem to be thinking of a web viewer app for the site, which isn’t the same as what I’m referring to. For example I’m using wefwef which is a good web app for mobile and desktop.