Next.js static server side rendering and Gatsby.js

Question

I want to build a website with Next.js and am trying to better understand their Automatic Static Optimization, and the different ways that you can use it.
So to start with, there's Gatsby.js which is a static site generator. When you run Gatsby's build command you get a /public folder which is completely static and can be deployed without any need for some kind of a back-end. If I understand correctly, this means that the entire static folder is sent to the client on the first request, and from then on everything, including routing, happens client-side.
With Next.js on the other hand, you have static generation, which means that all pages are pre-rendered on the server at build time (like Gatsby), but the application still depends on a back-end (either a full-blown server or a serverless function) for routing. I.e, the pages are pre-rendered but, unlike Gatsby, they're sent to the client per request, i.e on navigation. (I found this answer which says there's only the initial request with Next, but then, what's the difference from Gatsby?)
What I find confusing in all this, are things like Next's docs for Static HTML Export. They start by stating

next export allows you to export your app to static HTML, which can be run standalone without the need of a Node.js server.

So, sounds like this option gives us the ability to use Next just like Gatsby, i.e as a completely static folder.
But then they go on remarking that:

If your pages don't have getInitialProps you may not need next export at all; next build is already enough thanks to Automatic Static Optimization.

But Automatic Static Optimization refers only to server side static pre-rendering, and next build does not produce a Gatsby like static folder that can be deployed as a standalone.
So what am I missing here? What's the difference between Gatsby.js and Next.js? Does Gatsby can do something Next can't? Can I build a completely static site with Next without using the export command?
Most importantly, can I build and deploy a Next.js application with some pages completely static (like Gatsby), some pages only pre-rendered (getStaticProps and getStaticPaths), and some pages rendered server-side (getServerSideProps)?

Thanks a lot in advance!

Answer 1

The first request is for <url>/index.html so no the entire public is not sent to the client.

Gatsby optimises the loading process to ensure critical resources (HTML, CSS, JS) are loaded first, ensuring best possible user experience. From there it will load remaining resources required to render the full page and will also prefetch linked pages from the main page. Of course if you have requested a route to a different page, then the client would fetch the HTML initially for that page, but the process followed will be similar.

Gatsby is still better at this than Next.js (SSG is a very new feature for Next and this the core of what Gatsby does) - see https://dev.to/notsidney/gatsby-won-against-next-js-in-this-head-to-head-37ka.

In answer to your questions, yes you can do full SSG, partial SSR/SSG and full SSR with Next. You need to do next export if you want full SSG, otherwise for the other modes you are in standard Next territory and Next will take care of both SSG/SSR given you have a traditional web server running that can serve both static content and perform dynamic SSR.