The -z option is only required when creating packages which most users wont be doing.
Might I suggest you actually read the contents of
opkg-unpack before making such comments?
In any case, if
opkg-pack needs a certain version, then the dependency should be listed. It is irrelevant whether
opkg-unpack needs it or not, seeing as both are in the same
pkgtools package.
For normal package install the version of gzip provided by busybox is sufficient so a dependency is not required.
Possibly it would be, but
tar appears to hardcode
/mod/bin/gzip rather than just
gzip and therefore the version in
/mod/bin/busybox/ is not found.
In any case (again), there should then be a dependency on
busybox, which there currently isn't.
Do you think I posted the above without having checked?