[userbinator]

ZIP commonly uses DEFLATE which is LZ with a 32k window + Huffman, whereas LZH went up to LZ with a 64k window + Huffman. I suspect the doubled window alone is responsible for much of the improvement.

According to http://fileformats.archiveteam.org/wiki/ARJ , ARJ uses something similar to LZH's lh6 algorithm, which is LZ with a 32k window + Huffman, so the difference could be due to ARJ's reduced file format overhead compared to ZIP, or perhaps slightly better Huffman codes.