This is a very good point. The reason that you have trouble if you just use a bunch of scripts to start up a contemporary Linux is that the underlying system ha

This is a very good point. The reason that you have trouble if you just use a bunch of scripts to start up a contemporary Linux is that the underlying system has become quite complex. Now you have to deal with the effects of stuff like udev and dbus. Systemd can be seen as an attempt to paper over the underlying complexity problem with another layer on top. That of course if not likely to work but is depressingly common in the world of OSs. People add things to a simple system until it is no longer a simple system. Eventually it becomes unreliable enough that no one dares extend it further. As a nice counterexample, OpenBSD doesn't have stuff like udev or dbus usage during boot. The rc.d system they use is literally just a bunch of scripts and is dead simple and reliable.