The unit file format is what I don't like about it. A giant spaghetti code mess where dependencies can be literally anywhere and the final imperative result is completely opaque. An init system, ultimately, does a bunch of one time actions to bring the system up; it really does just work better as an imperative script.
An init system is for all practical purposes a build system - a very complex problem where literally every sane solution is declarative. Especially when you take into account error handling (that HDD is not yet available, will you imperatively wait for it to come up and pause everything else? Do parallel work in the meantime in fking bash? Or what exactly?)
Startup is ultimately a complex problem. There is no magic, just race conditions which maybe became more apparent. LVM may or may not be used, and takes time to start up. Do you wait for it? Ditto wireless networks. And how do you handle devices being hotplugged? Setups vary widely, and can be dynamic.
How are Systemd's unit files any worse than unconstrained init scripts written in a Turing complete language with even basic stuff - like PID files - managed manually?
Because they are opaquely translated into an imperative sequence but you never get to see it.
Also who are these people who have complicated sysv scripts? I've heard this for years and never really understood it. One script per service with a stop and start command (and maybe a status if you want to get fancy) and runlevel definitions that start and stop them. It's not rocket surgery, and it's a hell or a lot easier to debug than a declarative system definition.
The reality is that it wasn't corporate scripts hidden away from the public eye. There were some nightmare van Smoorenberg rc scripts in the likes of Debian.
FreeBSD has Mewburn rc not van Smoorenberg rc and was thus inherently better in this regard until the middle of 2014 (https://unix.stackexchange.com/a/480897/5132). But even FreeBSD has some large rc scripts, particularly in the networking and the HID parts such as Bluetooth and configuring all attached keyboards; albeit that the FreeBSD style guidelines mean that they are more legible than the nightmare Debian (et al.) ones.
