I think the author is unaware that `tar --compress-program foo` is equivalent to `tar | foo` (other than handling output writing and things. The analysis would

I think the author is unaware that `tar --compress-program foo` is equivalent to `tar | foo` (other than handling output writing and things. The analysis would have been much simpler, clearer and more focused on the compressor if they just benchmarked the compression with an already-generated tar archive. (Notably zip is different where files are compressed individually in the archive)