Deflated plaintext can be extracted (without inflating) from encrypted archive using
bkcrack -C ./foo.zip -c bar.xml -d barxml.bin --password password
But how to do that with unencrypted archive? Trying same with --password '' gives me
Zip error: entry "bar.xml" is not encrypted.

This route would potentially allow for identifying used deflate algorithm and parameters like compression level - assuming settings were the same between encrypted and unencrypted archives (so one plaintext to identify encrypted zip details, and another for known inflated file, that is deflated inside encrypted archive)