JXL decoding can still be optimized and had significantly less time for it, so let's not be so sure if that statement holds. Last update brought much improvement at just the area you mention.

And AVIF compression ratio beats JXL only conditionally. E.g. my photo library had AVIF at 29% and JXL at 25% the input size at the same perceptual quality (SSIM2=83). Sometimes it's on par. Sometimes AVIF wins. JXL wins almost always. Not to mention you can losslessly, reversibly transcode lossy JPG files to JXL, getting significant size reduction for free.

I think the case for JPEG XL is not that it's the best at everything, but that it is both quite good overall while also supporting basically every obscure image format feature under the sun. It's the potential USB of image formats.