MathJax3 question

I'm starting to try out MathJax3 with the rst2html5 option
     --math-output="MathJax https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"
as suggested here:
     https://docutils.sourceforge.io/docs/user/config.html#math-output

However, the resulting HTML file does not include the polyfill recommended here:
     https://www.mathjax.org/#gettingstarted

Looking at http://docs.mathjax.org/en/latest/output/browser.html leads me to believe
that MathJax3 is currently using ES5 and that the polyfill is only needed for
outdated browsers. And in fact, I am seeing ZERO problems.
So I suppose that leaving out the polyfill is a browser-support decision.

I am NOT worried about old browsers.
I would just like to confirm my understanding.

Thank you, Alan Isaac