It may not been the initial intention, but the aim of adding a layer to the OS does lead to what is effectively a new OS. Its a bit like MacOS vs BSD, or maybe Chimera Linux (Linux kernel with BSD userland) or Debian/kFreeBSD.

The best argument I have seen for systemd is that it adds a layer that will be used and standardised across multiple distros (most effectively in a video of a talk by a FreeBSD developer). The best argument against is that it is massive and does too much.