package myself; I chose Gentoo (and previously Arch) in part because its reasonably easy to package things there.
Most build systems are covered by eclasses ( libraries) that handle the repetitive minutia every package that build system needs.
Here’s the tuba ebuild for example (from GURU, the Gentoo equivilant of the AUR), 90% of it is just listing the dependencies and telling it to use a few eclasses to handle everything else.
kubuntu is already literally just a package.
if you just install kubuntu-desktop (or something similar) from any buntu flavor you get it.