I think this should include benchmarks zstd with larger windows and long range mode. I wouldn't be surprised if the window they used is smaller than an individual version tar file, which would prevent useful compression.
“Additional benchmarks on the same dataset” (2025) explores various compression levels with and without long range mode: https://news.ycombinator.com/item?id=42901476
“Additional benchmarks on the same dataset” (2025) explores various compression levels with and without long range mode: https://news.ycombinator.com/item?id=42901476