Not to detract from your argument (which I agree with), but SVG _can_ technically solve that problem using CSS. Here's a link that demonstrates this: https://tympanus.net/codrops/2014/08/19/making-svgs-responsi...
https://web.dev/articles/building/an-adaptive-favicon
Unfortunately, I tried the demo and even though it’s supposed to work in Chrome, it didn’t for me. Nor with Safari. Have you gotten it working with favicons anywhere?