systemd-journald is only one component, there are more than 50, and if you only want one piece of that, tough luck!
I'll just say, a GNU/Linux distro has many components, but they're not monolithic because they integrate well, you can do ls|grep etc, you know this. But if we want to change one component of systemd, we can't do it! You see? A lot of components, but they comprise a blob and can't be separated or used individually.