It used to be that everything in Linux was a file, ideally a text file, so if you could find the right file you could access or change what you wanted. Systemd is a big program that manages a bunch of stuff and creates unique commands within its programs for doing so, which moves away from that principle and turns system management into what feels a bit more microsofty (like the registry editor program vs editing config files, etc) and a lot of people don’t like that. But to its credit, it does solve a few problems with cobbling together a modern system that doesn’t suck.
Yeah but I’ve interacted with it a lot and most of my interaction is commands sent through one of their programs. Versus scripts like init.d whose contents I can easily inspect and modify. Init scripts aren’t config files, they’re directly executable code.