You are confused. I'm not sure why you were modded up here. NetworkManager is not part of systemd, and doesn't require systemd either. Your linux machines have been using it for years, several years longer than systemd has ever existed. Please get your facts straight before posting.
Sounds like your knee jerked and you mistook NetworkManager for networkd, which is a part of systemd. But networkd is intended only to provide simple network functionality for containers like Docker or virtual machines. networkd is not required, and I've never ever used it on my boxes and I've run systemd for years. I don't even think I have it installed (yes systemd really is modular and you can remove parts of it).
Possibly networkd could become a backend for NetworkManager, but so far I don't think that's the case. And NewtorkManager seems to handle hotplugging of devices with ease (like Wifi dongles or ethernet dongles).
NetworkManager is great for managing things like WiFi, VPNs, and multiple TCP/IP configurations. For example, I keep a special NetworkManager profile for connecting to my Ubuiquiti Wifi devices for the first time. The profile uses a static IP address like 192.168.1.10. For my normal connections, DHCP is used. NetworkManager is very powerful, and there's a nice command-line utility to interface with it as well. It used to be quite embarrassing for many years on Linux that even something as simple as plugging in a ethernet wire would not automatically bring up the interface like Windows and Mac had done for years. NetworkManager was a welcome piece of the puzzle.