You read the article incorrectly. Levinson states that the Madison, Hamilton, and Jay “mocked the ‘imbecility” of the weak central government created by the Articles of Confederation” not the proposed Constitution that came out of Philadelphia.
The piece is not bad, at least not in principle. We certainly should be having a discussion about the faults of the Constitution. After all, the opponents warned that by ratifying the document, Americans would be facing the mess we are in today. I do not agree with Levinson’s solutions (direct democracy, his proposal to allow the president to appoint members of Congress, etc), and I fear that Americans would want too much democracy and centralization instead of more federalism, but he is correct that the system needs to be examined and perhaps “fixed.” I included a list of proposed amendments that never saw the light of day in my Founding Fathers Guide to the Constitution. All would be worthwhile.