Them being disorganized to this point gives more credence to the theory that they aren't informed about Dilan, remember, going by Walter's secret cutscene, the nihtlings killing students and having Alan erase their parent's memories seems to be commonplace, you would think they would be told to back off immediately, not to mention only being watched after interacting with Macky, going by Occam's razor it's better to go with the simplest explanation rather than tack on assumptions on top of assumptions.
Dominic certainly knows the school's secret as evidenced by his journal, and it's not exactly straight up power that makes him dangerous, he's very smart and manipulative, has a huge network of allies in the Occult club, Vaila and even special boy Dilan, not to mention powerful abilities like mind control and portal creation.
The Nalid thing is just the way you're seeing things according to the route you took, in Nalid's case it's the "my own" path. He gets decapitated because that's what you're doing IRL, pick the Warmth route and Bonnie is there while you decapitate him with the pocket knife, pick the cold route and you'll have a cold dinner with Katja. Why tag? There's actually a broken event where you can play tag with Walter in school and gain cuteness, that's what the Nalid route is referencing.