Actually, the results of the AVIF team's comparison do show the value of JPEG XL, if you look a bit further than the main page and dig into the actual plots. E.g. according to this plot, JXL is about 15% better than AVIF for 'web quality' images (around 1 bpp): https://storage.googleapis.com/avif-comparison/images/subset...

Here is a detailed analysis: https://cloudinary.com/blog/contemplating-codec-comparisons