[kbolino]

A ZIP file with solid encryption (i.e., the archive is encrypted as a single whole) has all of the same tradeoffs as a KDBX file as far as incremental updates are concerned.

A ZIP file with incremental encryption (i.e., each file is individually encrypted as a separate item) has its own problems. Notably: the file names are exposed (though this can be mitigated), the file metadata is not authenticated, and the central directory is not authenticated. So sure, you can read that index, but you can't trust it, so what good is it doing? Also, to support incremental updates, you'd either have to keep all the old versions of a file around, or else remove them and end up rewriting most/all of the archive anyway. It's frankly just not a very good format.