One thing that's really great about JPEGXL is that it seems to be intended for use at the high end, e.g. larger files, more bits / pixel. Most of these newer codecs are based on the intra frame of video codecs, which are all optimized to look good at the lowest possible bitrate. (And even high bitrate video is usually much lower quality than what we use for static images.) I suspect there are a lot of easy gains to be had here, and actually I wish someone would look at doing a high quality royalty free video codec with the intent to target high bitrate applications. (It's noteworthy that a lot of professional applications like DCP use an image codec, JPEG2000.)
For anyone looking for some image comparisons between AV1 and JPEGXL, someone updated the classic "image format comparison" on Github and added it. [1] Important to note that all these are a little unfair to JPEGXL, because it's explicitly targeting higher bitrates than most of the quality levels you see here, and it still comes out looking pretty good at the higher bitrates.
I find JPEGXL much better at medium and large sizes for the sorts of artifacts that bother me, on most images. For example in this [1] comparison, AV1 is clearly degrained, losing the very fine detail.
Note that achieving high quality results at low bitrates is not really a goal of JPEGXL, or the codecs it's based on. For example the PIK readme contains the following note:
> It prioritizes authenticity, a faithful representation of the original, over aesthetics achievable by by hallucinating details or 'enhancing' (e.g. sharpening/saturating) the input.
So as I noted in the OP, it's not a very fair comparison with bitrates this low, but I think JPEGXL holds its own.
For anyone looking for some image comparisons between AV1 and JPEGXL, someone updated the classic "image format comparison" on Github and added it. [1] Important to note that all these are a little unfair to JPEGXL, because it's explicitly targeting higher bitrates than most of the quality levels you see here, and it still comes out looking pretty good at the higher bitrates.
[1] https://afontenot.github.io/image-formats-comparison/#abando...