MacGregor's point: we may be fighting counterinsurgency wars right now, as the British did during the 1920s and 1930s. That doesn't mean we won't have to fight organized, high-tech blitzkrieg-style attacks in the future, as the Brits discovered to their unprepared dismay in 1940.
To specialize in one or another type of warfare is to be unprepared for all others. To be unprepared is to lose or to win after great (unnecessary) trauma.
The bottom line is that a superpower must be prepared to fight any kind of war the future may deposit upon its doorstep, our doorstep. To be prepared is often not to have to fight at all; it is the best deterrence.