First, sovereignty isn’t in any level of government in the American system, but in the peoples of the separate states.
Second, the best books on the Articles are Jensen’s THE ARTICLES OF CONFEDERATION… and Dougherty’s COLLECTIVE ACTION UNDER THE ARTICLES OF CONFEDERATION (an overlooked blockbuster). For the question whether the Articles were really a flop, as the Federalists claimed, I recommend THE DOCUMENTARY HISTORY OF THE RATIFICATION OF THE CONSTITUTION, VOL. VIII-X: VIRGINIA. There, you’ll see Patrick Henry, William Grayson, James Monroe, and George Mason argue that no, they hadn’t been at length and in detail.
I deal with this question in one chapter 3 of VIRGINIA’S AMERICAN REVOLUTION (Lexington Books, 2007).