One weird subtext of this discussion is the idea that imprecision in the guidelines is costing "the subjects" something. But getting moderated doesn't cost you anything; on the contrary, it costs Dan. You just adjust and move on.
Quite beyond the quiz instructions, the rest of the psychology on display in this thread is fascinating. Having clear rules makes things harder because other people will follow them. That sounds like the kind of outcome you fear only if you don't really want there to be rules, but only cultural homogeneity. Which is a stated anti-goal of the site.
I really don't think HN does the best possible job of living up to this ideal as a consequence and you see this in the wide range of important topics that the site has largely failed to debate. For example, a common complaint on lab leak stories is that just a few years ago this site was routinely suppressing people who were attempting to engage in curious conversation about SARS-CoV-2 origins.
The HN approach makes things simpler for moderators in much the same way that being a monarchy makes lawmaking simpler for the king, but writing down rules isn't about making the enforcer's life easier, it's about making the subject's lives easier. They're more numerous, so their needs should have at least some weight.
Independent of that argument, precise written rules and a process for updating them are valuable for several reasons:
1. Whilst people might still get mad, they get mad at the written rules and not at the interpreter of them. This takes a lot of the heat out of the situation because a document can be improved easily relative to improving a person, so discussions about bad outcomes become de-personalized and more constructive.
2. The act of writing down rules forces mental clarity. Contradictions and unhelpful biases that may not be obvious when free-floating in one's head can become apparent immediately when trying to write it all down.
3. Because the rules are clear, violations are less likely to happen to begin with. People who aren't on-board with the values of the community stay away.
The generic HN prohibition against "flamewars" is a good example of a rule that could use a rigorous clarification. It doesn't work to assume the intent or definitions are obvious, because flamewar is a purely online concept that doesn't have any clear analogy to the physical world. Actually it's the opposite: in physical debates there's a general understanding that anyone who turns up and takes part will engage in emotional self-control. If they lose it and start getting angry or raising their voice, they're the ones expected to leave, regardless of what argument the other side was making at the time. HN's approach inverts this standard social convention and blames the person who remains calm for the behavior of angry respondents!
The thread you linked to (from 2015!) is a good example of this. The original post is something about pi and the Bible. It's phrased calmly, isn't obviously in bad faith and is at least somewhat interesting yet is flagkilled, then you threaten to ban the user for conducting "religious flamewars". That user quite reasonably asks what it is that makes his post a rule violation and gives several possibilities e.g. is all discussion of religion banned? But you reply that it would be "soul destroying" to answer his question that specifically! He wasn't asking for a mechanical algorithm but getting more specific than "religious flamewar" and "spirit of the place" doesn't seem like an unreasonable request.