data size

[setop]

Using unzip -p tranco_NNZPW-1m.csv.zip | awk -F, '{print $2}' | gzip > tranco_NNZPW-1m.csv.gz, I managed to shrink the file from 9.2MB to 6.6MB (2s elapsed time) and even 5.5MB using zstd -19 but then is take 20s to compress.

If having the line numbers are important, it can be rebuilt using gzip -cd tranco_NNZPW-1m.csv.gz | awk '{print NR","$0}' or gzip -cd tranco_NNZPW-1m.csv.gz | nl -s, -w1.