The problem isn't the common name, it's the tight coupling between components. This is antithetical to the Linux philosophy, which emphasizes modularity, interchangeability, and configurability.
I assume you mean the UNIX philosophy? Regardless, almost all of said components are optional, systemd doesn't in any way force you to use them. As a matter of fact many of the components you listed have alternatives that are more popular than the systemd tool (NetworkManager over systemd-networkd, GRUB2 over systemd-boot, etc).
Most yes, not all of them.
For example logind. Is there any reason why this should be coupled with systemd?
Apparently not as has been proved by elogind project.