And in that seclusion they missed out on the most important development in human history - The Enlightenment.
Two wrong conclusions in one sentence. Neither were the islamic world secluded (they were expanding beyond spain even after the crusades) nor did they 'miss' the so called enlightenment. In fact it can be argued that the european enlightenment was a result of the interaction of the dark age europeans with golden age of islamic spain (and other centers of learning during this time in the islamic world).
So instead of religion being a hindrance to the "light of enlightenment" to the human race, religion had everything to do with it. Especially if enlightenment is given a broader meaning than just ways of acquiring material capabilities and means of pleasure.