Have to wonder what those 20 MB SVGs were like and whether they could've been optimized as SVG still. Doesn't seem to add up that at "huge" resolution that PNG would be that small either.
What I mean is, if you have a million pixels of the same color (0xDEADBEEF maybe), then PNG will call that 1,000,000 x OxDEADBEEF. So, it scales very nicely for few-color, sparse or "blocky" images.
Well maybe not huge huge. Like 1000px wide so they look nice on retina screens.
The key is that these images were just 2 contiguous color areas. Black and transparent. PNG is really good for that because the compression algorithm works on the basis of contiguous color areas.