The Confederation could not pay for an embassy to Spain, could not pay the interest on its loans, could not pay the soldiers what they had been promised, could not raise troops, etc. In short, it was next to worthless. This isn’t to say that amendment could not have worked, but surely the situation in 1787 was untenable.
I had never heard of those authors prior to reading your query, other than seeing one of their books’ titles mentioned. I’m sure there has been no peer review: who are their peers?