This is most definitely not a steaming pile. The 10th Amendment reads, "The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people." In other words, if it's not in the federal constitution, the feds can't touch it. It's up to the states, or if prohibited by the state constitution, the people of that state.
The "dual" in dual federalism refers to the split of the powers between the state and federal governments. If the federal constitution grants authority, it simultaneously denies that power to the states. From Article 6: "This Constitution, and the Laws of the United States which shall be made in pursuance thereof, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding." Thus, the powers delegated to the federal government in the constitution supersede state authority. But such powers are limited to those enumerated.
This is not a difficult concept. To claim this is an invention of progressives is ludicrous. Yes the United States is intended to be a representative republic, but you have missed the point on the separation of the state and federal governments. There are two representative republics at work here, at both the state and federal levels. Each have separate powers and duties.
Of course, a lot of this theory has been perverted over the past 100 years or so by such groups as the progressive movement, so you are not wrong to excoriate them for dishonesty when it comes to American government. But I think you are missing the mark on this issue.