Turns out that these numbers are caused by APFS weirdness. I used 'du' to get them which reports the size on disk, which is weirdly bloated for some reason when

Turns out that these numbers are caused by APFS weirdness. I used 'du' to get them which reports the size on disk, which is weirdly bloated for some reason when compressing in parallel. I should've used 'du -A', which reports the apparent size. Here's a table with the correct sizes, reported by 'du -A' (which shows the apparent size): +---------+---------+--------+--------+--------+ | none | zstd | xz | gzip | brotli | +---------|---------|--------|--------|--------| | 47.81M | 37.92M | 37.96M | 38.80M | 37.06M | +---------+---------+--------+--------+--------+ These numbers are much more impressive. Still, Brotli has a slight edge.