... the goal of interpreting written documents has been what I mentioned before, historical, literal and grammatical. Deviation must be supported and justified by either the text itself or supporting context. We've drifted so far from the plain text because dragging in extraneous bits into interpretation has become de rigueur. The founders and framers most certainly did disagree, sometimes vehemently. However, once the document was written, it became subject to the same rules of interpretation as any other document. ...
You have not described a goal of interpreting documents. You've described a manner, i. e., "historical, literal and grammatical." What does that have to do with the deciding of cases by courts?
However, in real life in the real world, the the legal system decides, through judicial process, disputes, disagreements, controversies, or legal questions. Law, including constitutions, statutes, regulations, and decisions of courts of appeal, is a tool used by courts to decide the the issues brought to court for resolution. While the parties may argue what the law is that is applicable to the case, it's up to the court, in the exercise of its judicial function to decide what law actually does apply and how it applies to the facts to decide the outcome. As the Supreme Court ruled back in 1803 (Marbury v. Madison, 5 U.S. 137, 2 L. Ed. 60, 1 Cranch 137 (1803), 1 Cranch at 177), "...It is emphatically the province and duty of the judicial department to say what the law is....." It's been that way since long before the birth of this Republic. That's what English courts did in the 1700s. That's what U. S. courts (both state and federal) did in the 1800s. That's what U. S. courts do today and will do tomorrow.
The foundation of our legal system is the Common Law of England as described almost 300 years ago by William Blackstone in his Commentaries on the Laws of England. A basic attribute of a common law system is stare decisis:
...the requirement that courts follow decisions of higher level courts within the same jurisdiction....
Today law in United States comes from enactments of legislative bodies, like Congress or the legislatures of the States and case law (judicial interpretation and application of legal principles). See this outline of "Basic Concepts of American Jurisprudence."
In real life in the real world if courts aren't deciding matters using what you think the law is, your understanding of what the law is is wrong. The opinions of courts on matters of law affect the lives and property of real people in the real world. Your opinions and $2.00 will get you a cup of coffee. The fact is that no one cares about your opinions, and the world is going about its business, and will continue to do so, without regard to your opinions.