It’s not proof, true; your point about l’chatchilah vs. sha’as had’chak is a fair one, but the point is still true.
Plea bargaining means accepting punishment A for crime B (or for the accusation). It does not mean admitting to crime A.
When someone responds to a specific point, it doesn’t mean they have not heard other points. It only means they didn’t respond to it.
I brought up Rubashkin here only because the other thread was closed, and wanted to dispel possible motzi shem ra. Don’t use that against me; that’s unfair.