My pet view is that the fundamental flaw in the Constitution is its decreasing ability to enable coordinated change as population grows and more states enter the Union. Thus, change becomes progressively more difficult over time, whereas changes are increasingly necessary as time passes.

Yes, one of its main goals was to make change difficult. But political-party and legislator capture of the system has taken hold (easy example: representatives now pick their voters) and coordinating amendments we need is nigh impossible.

Periodic constitutional conventions would have helped.