What really makes people shocked in "Three-body" is the imagination behind it, as well as the insight and satire on the contradiction between social life and human nature, but it is not the logic behind it.
The Dark Forest System is very well written, but we should realize that this theory cannot be derived from only two axioms. There are also many hidden small D settings, such as the explosion of technology and the crowded universe. These two axioms are not 100% correct. For example, survival and expansion are really the first needs of the development of civilization, then the ETO and three-body observers of the earth should not appear.
The secret of mystery novels should be:
This method exists in real life, and the clue is given to you, but you didn't expect it. "Three-body" is a clue for you, you really didn't expect it, but this thing doesn't exist in real life (at least not sure).
So the two-way foil is shocking, but the three-body is science fiction rather than reasoning. If measured from the perspective of mystery novels and tricks ... this is a perfect secret room murder case. Finally, the mysterious solver knows about magic. He locked the door with Harry Porterie's lock spell. Even if you plant the seeds of magic in this world in advance, it will be regarded as the shame of mystery novels.