of course these are all fairly controversial claims

- people dispute it compresses meaningfully better the types of images typically found on the web.

- progressive decoding is increasingly less useful on the internet as more and more connections become latency limited instead of bandwidth limited. jpeg & png (Although png's version has a cost i think) both support progressive decoding. However the last time i saw an image actually progressively decode was probably mid 2000s.

-flexibility in file formats is usually a bad thing. look at tiff.

personally i think jxl is massively overhyped. Its not horrible by any means, but its only marginally better than existing stuff, at best.