You are quite correct, if I correct the original file the gzipped equivalent of the file ends up just 4% larger, so the gap between the two narrows quite a bit.

You are quite correct, if I correct the original file the gzipped equivalent of the file ends up just 4% larger, so the gap between the two narrows quite a bit. Still a bit of fat to trim but by no means the same level of waste the raw file contains.