In my experience, systemd is much better documented, way more consistent, and way more reliable than what came before.
Maybe, but the scale of systemd features is humongous. It better be well documented. You don't need a user manual for hammer, you do need one for hydraulic press.
Well, in my experience, systemd has much worse documentation, is very inconsistent (or you could say it is constistantly brain-dead), and extremely unreliable and unpredictable, since it often hangs when shutting down and rebooting.
So, I disagree about your statement here, but let's for a moment assume it were correct - so let's not evaluate THAT particular statement, thus.
You most likely refer to sysinit or something like that, right? Because to what else do you compare it to? Shell scripts?
Shell scripts in general are crap. I don't understand why linux systems use them. When I transitioned to linux a long time ago, I wrote - and still write - pretty much all logic in ruby and .yml files. Literally my whole system is described via .yml files, ruby then just auto-expands all of this into what is meaningful. I also compile from source and manage the system via ruby as-is, so I don't even need systemd, nor shell scripts. But this is just one comment here and if you refer to shell scripts then I agree with you - shell scripts have always been horrible. I fail to see why we should like systemd merely because shell scripts are so awful. That makes no sense. I neither use systemd nor shell scripts (ok ok I bail ... I am currently using manjaro which uses systemd; I disabled most of the services, but the primary reason I was assimilated into systemd is mostly because the non-systemd linux distributions, kind of gave up for the most part or come with their own set of problems - slackware, void and so forth. And yeah, I was using and testing them for ages too, slackware I used for many, many years. It is still a great distribution but it is not really active anymore. No new .iso releases in years, sorry, that is dead. Even if Patrick still updates packages.)
The other part is ... IF you referred to an alternative init system, then THAT comparison is flawed too, because sysvinit is mostly just an init system. Systemd is some giant thing that does 100000 things. So the comparison is, and ALWAYS has been, unfair. Not the same things are compared here.
I guess it depends on your source of info but I've found what came before was pretty comprehensively & accessibly documented, at least as well as systemd, which - while well documented - suffers from sprawl & overwhelm of the docs. There's just SO MUCH to grok in comparison.