By the way, reading this, an idea just hit me. It persistantly seems evident distro maintains often struggle to maintain huge repositories in both well-tested and up-to-date state. Why don't we separate OS distribution and apps repos into separate independent projects

Because applications rely on libraries in the distribution and need to be in sync for when they change.

Ways around this are Flatpak, where those shared libraries for applications are shared runtimes that are distro agnostic.