Again, it's not quite that simple. The amount of heat transferred is proportional to the storm's intensity; by modifying storm intensity -- taking the SSTs down to 70-75F would not lead to category 1 storms, it would lead to almost no storms, with the caveat that SSTs are not the sole factor toward TC intensity -- you would be changing the heat transfer across the globe.

Water temperatures are not constant with depth; in fact, they are far from it. Further, the annual cycles of SSTs plus the change in SSTs with depth play a key role in maintaining stability within the oceans and supporting all manners of life, whether on land or in the water. How exactly do you propose doing this over a (rough estimate) 6.25 million square kilometer region in the Gulf of Mexico, anyway? The cost of such a system just over the Gulf of Mexico to work effectively -- never mind the inherent problems to the "solution" -- would be well into the billions of dollars, if not trillions, and likely would not work even then. Do you have any idea of the amount of water that would need to be affected over just a 1 mile x 1 mile box in the Gulf, or the amount of pipes & mechanisms needed to effect this change over reasonable length scales? It's much, much more than you would think.

What about other regions of the globe, both in the Atlantic and not in the Atlantic? What about midlatitude weather systems? Many people depend upon the sea for their way of life, and by changing that you would be eliminating their way of life. I could go on, but as in most facets of life -- things are not as simple as they would seem.