It wasn't just "concocted" as a figleaf to cover up some supposed "error" in theory. The theory of punctuated equilibrium was actually developed by Stephen Jay Gould and Niles Eldredge to explain the exact opposite: the apparent monotony of the fossil record; that is, Eldredge and Gould set out to try and explain why the fossil record looked the way it does and why there wasn't apparent gradualism in the fossil record.
The explanation is, to summarize it (almost to the point of bowdlerizing it), that once a new species develops, it's form quickly stabilizes and thereafter most genetic changes result in slight genetic drifts and "wobbles" that nonetheless do not deviate too far from the original form of the species.
As to the (mis)use of punctuated equilibrium to "support" the myth of intelligent design or creationism, I think that Mr. Gould's words
speak for themselves, and for him.
If punctuated equilibrium supposedly accounts for ending of the pre-Cambrian stasis, and that the Cambrian explosion occurred in a very short [geological] time frame, how do you explain a half billion years of (for all intents and purposes) a post-Cambrian stasis?