gzip is not an archive container. You're thinking of .tar.gz which is a "tape archive" format which is compressed using gzip. Zip is by itself both a compression and an archive format, and is what documents like epub or docx use

You are right, but other documents like .ggb (GeoGebra files) or .mbz (Moodle backups) use the .tar.gz method. I even wrote programs to opened them, make a few tweaks and save the new version in another compatible file.