I'm still going through the link, but I think I can answer your question in the general sense. In creative writing classes you get a lot of rule of thumb advice

I'm still going through the link, but I think I can answer your question in the general sense. In creative writing classes you get a lot of rule of thumb advice similar to what's being talked about here. The reason it's a rule isn't because you're not supposed to break it. The reason it's considered a rule is to discourage students from using a particular theme, technique, or idea as their primary tool at the expense ignoring growth in their personal areas of weakness. It's not assumed that the student will follow the rule once they've finished the course. But during the learning period they're discouraged from breaking the rule because the overarching goal is to have them develop a broad technical skill set that they can then refine back down into their own particular style.