I would add - making handling of forking to the background and log rotation not a task of the program itself, instead of making every program (or worse, a besp

I would add - making handling of forking to the background and log rotation not a task of the program itself, instead of making every program (or worse, a bespoke wrapper shell script) do it. Because such things are non-trivial and demand reasonably many man-hours of otherwise "trivial" projects. Granted, you don't actually need systemd to do such things (for example, runit can do such things, and runit is available under busybox and therefore almost universal in most GNU/Linux distros), but I think it was systematic distro/systemd that enforced such new paradigm.