My understanding is that if you want to avoid the occasional oversmoothing artefacts when using AVIF, you need to turn off many of the tools giving compression

My understanding is that if you want to avoid the occasional oversmoothing artefacts when using AVIF, you need to turn off many of the tools giving compression density. For example main smoothing tools have control fields that govern 64x64 pixels at once -- so you end up having either too little or too much smooting in some areas. In JXL the respective smoothing control field is 8x8, so you have much more opportunity to do the right thing.