Well, looking around the internet, one of my questions has been answered.
It was:
"Why didn't Dassey's defense team use the arguments of Kratz during the Avery trail, against him during Dassey's own trial?"
Well, it turns out, that the
Judge wouldn't allow it. Apparently statements by prosecutors, even if they are made about other defendants in the same crime are not admissible as evidence in a case.
So essentially, it doesn't matter that Kratz literally said that "Only one man could have killed Theresa Hallbach!" or that the theories of the murder are conflicting. The prosecutors can say whatever they want in a trial and not get called on it in a follow up. How the HELL is that legal?