That's correct, but it's important to keep in mind that JPEG XL is tuned for high quality images. If your baseline is heavily compressed JPEGs or AVIF images, switching to JPEG XL might save you nothing at all. However, if you're starting from 4+ MB high resolution JPEGs, and looking to save bandwidth while keeping the same quality, JPEG XL is vastly superior to anything else (including AVIF and WEBP).

JPEG-XL is not really any better than WEBP. You need to be using AVIF "significantly smaller", just a shame that Google's online AVIF compressor sucks so-much (Wrong compression mode and uses the AV1 default artifact blending (Chroma Sharpening which is not really sharpening or even just for Chroma but actually sets the artifact blending. 0 is default for AV1 and tries to hide all artifacts, increasing to 3 which shows all artifacts).