Considering this is Mozilla and they were the first major organisation to call out Webp and supported JPEG via a new encoder, it does give more weight to the comparison between JPEG XL and AVIF.

Prior to 2024 JXL were the better codec for image with BPP 1.0 or above. AVIF or AV1 itself has had a lot of quality improvements since then. May be this has change. Which means more testing needs to be done.