You are conflating curation/QA and packaging. Packaging itself should not care about the quality of the packages.

It's well known that the debian repositories are extremely well reviewed and tested. But you could have that with Arch's packaging system as well.

When someone builds a package themselves however, they are not expecting Debian's QA & testing nor are they usually interested in it. But a package, untested as it may be, is far, far better than a sudo make install.

When I used debian this was such a huge pain. Building packages was not worth the hassle so I would simply sudo make install and feel awful about it, and end up with conflicts and everything that a package manager is supposed to solve...