Hmmm... bucking history a little bit here. Carter is certainly worse than Hoover, who was a great man that has been unfairly tarred by revisionist rat history. I would say that Wilson was an awful president, but he did successfully prosecute a world war, and he didn't really fall apart until he had the stroke. Taft wasn't too great, but face it, it was hard to cause the same kind of damage in the 1900-10s that Carter did in the 70s.
I think you'd have to go back to Grant to find a potential worse president than Carter and an exemplar of the old bromide that great generals make lousy presidents.
The way liberal historians have highjacked history, I would be wary of making the claim without first hand knowledge. Since none of us were alive then, I stick with my first opinion.