IMO that 99+% of the work done upstream is the cross-distro collaboration

Distros are their own "upstream" traditionally for system configuration utilities (think YaST), application install GUIs (what this sprint was about) and of course the low-level package tools (zypper, dpkg and what comments in this thread are obsessed with).

With the first two groups there is a lot of needless duplicate work. There are certainly cross-distro projects in those areas (NetworkManager comes to mind; its mostly "distro devs" not upstream devs that work on it), but more work could be done.

Its fine to have a software ecosystem of competing projects, but there is a finite supply of open source developer hours. They should cooperate when they can.