I don't understand, did you read the article? The ambiguity was resolved. The board ruled against Amazon. It's just you left arguing some absurd "what if", no part of which makes any sense; Amazon has the funds to pay all the infinitesimally many "bad worker that joins the union drive to avoid being fired" people till the end of the millennia, an obviously better strategy than firing them on bad excuses only to have them publically reinstated with back pay.
The labor board isn't actually part of the government, and it's decisions aren't binding. It's decisions are routinely overturned by later lawsuits. The mere fact that the board made a ruling hardly solves any ambiguity.
The National Labor Relations Board is a federal agency created by an act of Congress. No, they are not the Supreme Court. The acts of every federal agency are subject to judicial appeal. Generally speaking, you cannot file suit in federal court against the government until all administrative appeals are exhausted. Congress created the NLRB to administer federal law in this area and they are the only avenue available, barring some state law perhaps.
There's a process in the justice system called mediation. Basically, it's a session where the plaintiff and defendant get together and have a discussion about how to resolve the conflict. It cannot, however, make binding judgements. Only a real court can do that. If the two parties disagree then it proceeds to a lawsuit.
The NRLB processes mediation for labor disputes. Its decisions aren't binding, and it's common to proceed to a lawsuit or arbitration even after the NRLB rejects someone complaint.
