Can confirm that the React beta docs do not use Docusaurus, and it 100% makes sense to me. I've explained why here: https://twitter.com/sebastienlorber/status/14527225683902218...

Note that we also want to explore if Docusaurus could run on top of Next.js, Gatsby, Remix, and eventually become framework-agnostic.

The Docusaurus team is relatively small, and can't really compete with Vercel/Next.js on the static site generator infra, build performance etc... Until now we mostly focused on implementing a good set of flexible docs feature.