In all honesty this proves precisely the opposite of the point you're trying to make. New York requires that kind of investment in its defense to protect it from naval attack. It's not necessarily a question of if the Royal Navy can sail up and take New York City, but of the scale of the forces that have to be reserved to protect it. If those forces are protecting New York, then they can't be used for something else. And if you take them away from the City to do something else, then the Royal Navy can sail in and take the city. So it's a matter of the opportunity cost, as well as the financial expense, of defending the city, because New York is vulnerable. Moving the capital there just makes it even more so, because the cost of losing it is even worse. So you need to defend it with even more forces. And as a consequence all of those soldiers and guns are spending the war sitting around New York, instead of doing something useful somewhere else where they might be important.