More correctly, you can't just use networkd as your dhcp client unless you have systemd as init. You could however use dhcpcd on top of systemd (tho the latter would likely make a lot of noise about "missing functionality").

And that is the insidious nature of it all. the *d's panders developer laziness. What do you do when some production critical piece of code demands networkd, logind, or any of the systemd sub-daemons? Do you look to replace it, or do you roll over and replace whatever already functioning init you have with systemd?