Lack of passage of an amendment proves nothing since Congress already had the power to prescribe laws in Article IV, Section 1. They may have needed an amendment to make secession illegal though. If states would follow Article IV, perhaps secession would never be necessary.
Let's come to an understanding of terms.
There is a hierarchy of levels in the law, many of which we never deal with.
The highest level is sovereign acts, the kind that can be reviewed only by Who Am. These are acts of will by the Sovereign, who in England is the King or Queen.
The next level is constitutional and treaty law. They are made by the Sovereign and obeyed voluntarily by the Sovereign. They can also be broken by the Sovereign, by sovereign acts.
Under the Constitution is statutory law passed by the Government created by the Constitution.
Beneath that is regulation lawfully created by bodies created by statute and reviewed by them -- by e.g. administrative law judges and inspectors general.
And below that, there are other rules and guidelines that lawyers and regulators can describe in better detail than I.
My point here is that under the logic of subsidiarity, a creature of the Constitution, i.e. the United States Government or its branches (Supreme Court, Congress, President) cannot review an act above its pay grade, i.e. above its level of competence. When the People sit in convention assembled, they take up the rods and axes of the Sovereign and become not objects of government but take on their awful aspect of Sovereign, and in that capacity, the People answer to nobody who isn't God Himself. Capiche?.