If you look at the plots in the 2nd link you are referring to, they show the gains of AVIF over WebP are also similar, so the case of AVIF "isn't a sufficient i

If you look at the plots in the 2nd link you are referring to, they show the gains of AVIF over WebP are also similar, so the case of AVIF "isn't a sufficient incremental benefit" as well by your criteria. Not to mention JPEG XL can do lossless and progressive on top, and that avifenc is much slower than cjxl.