AFAIK Safari was the first browser to support MathML fully, and FF also supports it. Chromium was the latest IIRC. MathML has been baseline-available since 2023 after Chromium got support.

The big issue is that MathML is designed as a target language, not something directly writable. So we still need a KaTeX equivalent, which compiles either LaTeX equations or other markup languages to MathML.

Regardless, the core issue that you have mentioned is now gone (or will be in a few years even if you want more availability).