The alterative is an old school style web server that returns a new HTML file and page reload on every navigation which is higher download and runtime cost (which is how the real HN does it!). No criticism here as the site definitely works well regardless.
If you disable JS on the client and load a Remix app, the app will still work (though not as fully). You'll still be able to navigate links, load data etc. That's not true of most other apps built in just React that do all their data fetching client side and store all the data client side.
I mean, it's true for any halfway competent implementation of a React app with React Router and SSR. I love Remix and I agree that it offers a great dev experience and will probably make developing React Router SSR apps much more accessible to a lot of new devs. But this particular aspect (SSR with nested routes that each have their own data loader function, and links that are actual <a href="" /> links) is, like, the bare minimum functionality you'd have in an SSR React app 5 years ago. I always feel like the Remix team is massively underselling itself when they focus so much on "we have SSR with nested routes!" instead of focusing on the real innovations that Remix brings to the table.