> systemd and libsystemd is an absolute mess

how? Because they link against a third-party library?

> is there a dependency graph that would show how many programs use a specific utility library

Agree, important topic

> is there a dependency graph that would show how many programs use a specific utility library

Depends on the distro, but your package manager should be able to do that. On a global scale, that's likely impossible, because there's no true register of how programs are linked - in fact, the inclusion of libsystemd was distro-specific