> React supports rendering to HTML ahead of time (SSR)...

So does XSLT?

Literally not one person said XSLT can't do it. But in case you missed it somebody did said React can't do it and so XSLT is better.

> build step with React and webpack and javascript absolutely required on the client-side

This was a false statement.

both XSLT and React can be used for this except React can additionally do a bunch of other stuff that does use JS and that XSLT can't do.