"When we reach a situation where some unknown person pushes an upstream update, which causes a cascade of problems that even someone with deep technical knowledge and daily connection to the project cannot unpick, that's a breakdown in modularity/dependency."

Agreed. I believe that the "UNIX philosophy" is a good strategy for avoiding these scenarios and I believe it is underappreciated - even by architects and designers that should know better.

Forgive me for injecting this word but this is why I recoil so violently from systemd and all of its accoutrements. I can sense how this is going to fail even if I can't clearly elucidate it just yet ...