The author isn't wrong, and such issues are worth thinking about when either running campaigns or doing #ttrpg worldbuilding. At the very least, dungeon inhabitants tend to be people or creature who live in this marginal environment because they were pushed away from more fertile regions (such as the fertile surface lands typically inhabited by player character ancestries).

Even if you do use some of this default structure, it's worth introducing some scenes and elements that could make the PCs (and the players) think: "Hold on, are we actually the good guys here?"

@juergen_hubert @naught101 yeah, the author isn't wrong, but this line... Uff..."and it’s not just d&d. old-school essentials, for instance, makes the structure even clearer..."Clearly someone who only ever played 5e D&D.