Yes, the Arch docs are the best. But they aren't from the systemd project itself, are they?
These sorta landmines when trying to just research/digest a concept can really suck. OP's tool really eloquently breaks things down to _just_ core concepts so you can quickly start to grok what I consider to be a relatively complex tool.
Overall I use the Arch wiki very often and it's because of the exact point you're making - I'm just being pedantic saying those slight distro differences can be a pain.