I'm working on a site right now that doesn't do any SSR—it's just an index.html with a bundle.js on it. Google indexes it fine and surprisingly we have great SERPs. 2nd result for "trillion trees"

It is perhaps possible that google indexed it from a previous version that did have html, or they are using a sitemap.

(I've just joined the project, and I intend to get them set up with proper SSR soon.)

I'm not sure I entirely agree - Facebook is mostly login-walled anyway and they developed React to suit the needs of a data intensive SPA. Why not just use a robots.txt to stop crawlers from indexing?

Sarcastically, React server side rendering works much better than the others like Angular.

It's that easy - just one liner to use it in ExpressJS and a server side template system.

In a similar fashion to React itself, it's not that easy once routing, caching, context data, request or query parameters, data fetching and state management, environment variables, sessions etc all come into play.

React has a server-side rendering API. So, I find it difficult to rationalize an argument where FB purposefully launched React to get people to return virtually empty HTML documents from the server (at most, a script tag which "boots up" the page content) in order to make the task of indexing difficult.

Facebook indexes many sites themself for link preview functionality. Preview images, page title, description are all derived from open graph tags.

Did you read the article? There's a whole section on SEO that talks about how it works great with SSR.