This doesn't strike me as a well-considered objection to the practice of banning torture.
First of all, I'm not sure it's true that our torture ban represents a strategic disadvantage. One of the reasons that the Sunni tribes were willing to turn against al Qaeda in Iraq was because of its reliance on torture. Even in the wake of the Abu Ghraib scandal, that we were less likely to torture our opponents horribly (and showed an appropriate sense of shame about our lapses) made it easier for Sunni insurgents to consider walking away from the hatred of years of conflict with us, and consider a new partnership.
Second, even if it were true that a 'torture gap' was a strategic disadvantage, it may be that we could afford a strategic disadvantage given our other strategic advantages like the possession of a real air force. If so, we might be willing to accept the small cost in order to uphold our moral principles. This one is pretty important. It's worth paying significant costs to maintain.
In general I oppose trading moral principles for economic gains. If however you are the kind of person who is so invested in an economic mindset that you must sell off valuable moral principles, at least you shouldn't sell them cheaply. You should get a better deal for our principle against torture than beating ISIS, which is soon to be Russia's problem anyway as the current administration will have finished conceding the entire Middle East to Putin before you take office.
Third, I am deeply suspicious of the government's capacity to avoid sliding down slippery slopes. It has proven over the last two decades that it is inclined to do so. Removing the law against torturing terrorists suggests removing the law against torturing some despised classes of Americans, such as perhaps drug dealers. Removing that law suggests widening the class of despised Americans against whom torture can be wielded, perhaps to include "racists" or "sexists." Given the government's propensity to sludge down to the lowest level it can find, we should be reinforcing these walls rather than weakening them.
I could go on, but this surely suffices.