It is a cherry picked data point, and not representative for brotli. There, facebook shows numbers with quality 0. However, when they compress for the web, they

It is a cherry picked data point, and not representative for brotli. There, facebook shows numbers with quality 0. However, when they compress for the web, they use brotli with quality 5 for dynamic content and quality 9 (or 11?) for static content. At higher quality settings brotli wins in compression density, and particularly so with quality 11 or with short files. Quality 0 is an irrelevant corner case of maximal compression speed, and is completely impractical for most uses. If you plot the whole curve, brotli's density is above that of zstd's for compression speed/density -- when both algos are used with same backward reference window size.