I wouldn’t recommend relying on Safari MathML rendering today for anything but very basic equations. Firefox is a lot better, but still not quite at MathJax quality. I made a demo here https://mk12.github.io/web-math-demo/ that lets you compare them. Also if you edit the MathML markup box, it will render directly from that, just like the poly fill (sometimes the layout shifts slightly when switching from TeX -> MathJax HTML+CSS to TeX -> MathML -> MathJax HTML+CSS).