That's not really a disagreement, just another way of looking at it. It's clear that "traditional" Islamic culture is a major impediment to economic progress.
But a very important one. It is the impediment to economic vitality, and has been for centuries, after Europe changed the paradigm of economics: slaves and booty were no longer the machine that drove cultural dynamism.
It's sad that even Dr Sowell, is afraid to name the 10-ton elephant in the bathroom, but chose instead to refer to the symptom of the cultural disease.