moish, there is of course a great deal of subjectivity to rulings and interpretations. But that is also true in Halachik court – the dayyanim make their decision and that is law – but different dayyanim could have ruled differently. So I’m not sure how that point ridicules the American justice system.
Also, if you want to go back to the Beis Din Hagadol, the same type of variance in rulings could have existed. Let’s say that someone is brought to beis din and all the judges rule that he is to be put to death. The Halacha is that he goes free. If one of the judges sees reason to acquit but all the others rule that he is to be put to death, he is put to death.
The interpretation of the judge is the law in the courtroom. If you, as a party (and not as a juror) feel that his decision is a misinterpretation of the law, you are able to appeal his ruling. If the appelate court agrees with you then the decision will be overturned. But to the jury, who almost 100% of the time has an inferior knowledge of the law, the judge’s opinion IS law and they must treat his opinion in that way when hearing the case. This doesn’t make the judge’s opinion into THE law, but it makes it law, persuant to an appeal.