Man, I should have done this — would've been a much nicer number for the headline. Thanks for the analysis, though, this is really cool!

I compared it to image in PNG and QOI formats [0]

    img:         13.552kb (100%)
    img.png:      1.877kb (13.8%)
    img.qoi:     10.316kb (76.1%)
    img.qoi.gz:   1.167kb (8.6%)

While it does compress by 50%, it's not a format optimized for compression unlike png or qoi

[0]: https://qoiformat.org/