Kathernie, you will get more conceptions carefully reading these definitions:
https://access.redhat.com/articles/754933 (https://access.redhat.com/articles/754933)
The systemd system and service manager is responsible for controlling how services are started,
stopped and otherwise managed on Red Hat Enterprise Linux 7 systems. By offering on-demand service
start-up and better transactional dependency controls, systemd dramatically reduces start up times.
As a systemd user, you can prioritize critical services over less important services.
... More than services: Instead of just managing services, systemd can manage several different unit types...

https://www.gnu.org/software/shepherd (https://www.gnu.org/software/shepherd)
The GNU Daemon Shepherd or GNU Shepherd, formerly known as GNU dmd, is a service manager that looks
after the herd of system services. It provides a replacement for the service-managing capabilities
of SysV-init (or any other init) with a both powerful and beautiful dependency-based system with a
convenient interface.

Of course, 'system manager' systemd pulls the responsibility of whatever you want even boot logs and more than services.
In Russian forum linux.org.ru people dislike it. But it is using in some FSF approved systems (f.e. trisquel).

Did you read LFS book? There, system is building from scratches. That way is when you have no those strange layers with 'system managers'.
April 6, 2019 9:21 PM, "Katherine Cox-Buday" <cox.katherine.e@gmail.com (mailto:cox.katherine.e@gmail.com)> wrote:
  znavko@disroot.org (mailto:znavko@disroot.org) writes:Hello, Katherine! I've tried a little systemd, openrc and now I am
using GuixSD with shepherd. Lot of people and developers use systemd.
Here it is a link you may get info from
http://without-systemd.org/wiki/index.php/Main_Page (http://without-systemd.org/wiki/index.php/Main_Page) Here some theses
https://ihatesystemd.com (https://ihatesystemd.com) it was interesting for me cause I am not as
deep in init systems. 

While I would not characterize myself as a sysadmin, nor an init system
expert, I use systemd just about every day. I'm familiar with the
generalities of how it works, and why.I think need to define criterion to get appreciation of something.
Think that layer is not a criteria. Systemd works fine for some cases
when you are sysadmin that want to control lot of things in one
general interface - init system. 

I think it does more than to serve a unified interface to sysadmins. For
example, its built-in DNS server can dynamically update a `resolv.conf`
which some systems symlink `/etc/resolv.conf` to. This allows systemd to
handle signals of connecting to networks or VPNs, and update the systems
DNS servers dynamically. The acceptance of these types of signals and
the actions they spawn are what I think make up the "system layer" Benno
Rice was discussing.

--
Katherine