Up to 46% compared to PNG is more than a bit extra. It's also supports both loseless and lossy compression and supports backwards compatability between legacy JPEG. Among many other modern features.

And PNG is so old that it lacks basic modern features like HDR support.

The only competition to JPEG-XL is AVIF. Though both likely to coexist as they have different strenghts.

Here's the white paper on it https://ds.jpeg.org/whitepapers/jpeg-xl-whitepaper.pdf

Their dumb counter argument was AVIF, for the same reason as webp which is reduced total size since they're a massive cloud provider and want to penny pinch costs wherever possible.

JPEG-XL also has a progressive loading algorithm that increases the quality as you download instead of classic vertical scan loading, which is sick but I don't think any browser actually bothered to implement it yet after the Google hit job.

Hopefully will see it in action soon.

chromium gets jpeg xl support, a more superior alternative to jpeg and webp