As for previous court decisions, I would say these are (more or less) legal opinions, as well. Indeed, they are opinions as to how to apply the law given certain facts and circumstances.
this is correct. thats why doing things like citing laws and prior court rulings is argumentative, not evidentiary.
Let me understand properly, you're saying is that the law applies by definition?
No, im saying that whether or not the law applies to a specific circumstance or person can only be established with legal argumentation. Not with evidence. You might not think this is the way it ought to work, but this is the way it does, in fact, work. That's why judges, not juries, decide issues of jurisdiction.