There are some valid critiques, like dssim being an old and questionable metric, and AVIF using unoptimized settings, and maybe JXL having an "unfair" advantage

There are some valid critiques, like dssim being an old and questionable metric, and AVIF using unoptimized settings, and maybe JXL having an "unfair" advantage depending on how the source images (jpegs?) were ingested. But this is a real world benchmark. If this is an example of how a seasoned backend dev would typically set up AVIF and JPEG XL, its extremely telling.