The problem is that in many server environments, particularly at scale, the speed of the bootstrap processes of the OS doesn't matter. One of the goals of systemd is to make the bootstrap process faster, which is irrelevant for those (non-desktop) use cases. So you see, systemd is solving problems, and making trade-offs to do it, that just don't matter for the non-desktop use case. I can of course choose not to install gdm, but that doesn't change the fact that systemd was designed (you might say over-designed) with the desktop use case in mind. Because of that, I have to live with those trade offs, even though my use case does not benefit. Since all major Linux distros are deciding to adopt systemd, it will be very difficult to "roll your own" and use something else, especially since the rest of the userland will assume that everyone is doing things the systemd way, this making it even harder to go against the flow.