It should be neither. It should be a set of rules that most people can agree on. If some of that is what systemd does, that's fine. If there are things that systemd does that most people don't agree on, something else should end up in the standard, and systemd should conform to it.

The problem is that systemd evokes some pretty visceral negative reactions in people. I still have mixed feelings about it, but, by and large, I encounter minimal real-world issues with it. Just because systemd has decided to do something that violates the older FHS3/4 standards, doesn't automatically make it a bad thing. Maybe what they're doing is a better way. Maybe not.