Yeah, AVIF seems to remove noise fairly aggressively, or what it assumes to be noise. I think it looks pretty good in this sky example, although not overly faithful. It's less good when the removed "noise" is actual high frequency detail, e.g. on the fur of animals.

But what I meant with AVIF being good at homogeneous surfaces is that it apparently uses them sometimes to "save" bit rate, and to use it instead in other portions of the picture. Images with large surface portions tend to look significantly better in the rest of the image, e.g.

https://afontenot.github.io/image-formats-comparison/#clovis...

https://afontenot.github.io/image-formats-comparison/#us-ope...

I think here AVIF "small" looks overall better than JPEG XL "medium", e.g. in the details of the middle balloon basket, or the face of the tennis player.

I still think the lack of any progressive image loading makes AVIF completely unsuited for the web. The picture will only show once it was downloaded completely. That's a big step back from JPEG, and even more so from JPEG XL.