These really do not promote the development of subtle fighting skills that are difficult to train, and are for small / weak people to use against larger. Much better off taking the largest and toughest young men, teaching them simple and easily trained skills, and putting your resources into developing methods for organizing and directing fighters, and working out how to feed and equip them.
The truth is probably closer to the opposite - the internal skills come out of relatively lengthy periods of peacetime, during which professional warriors need something to show for all the time they spend not doing something else useful for society like growing food.
I'm not so sure. At the last seminar I attended with Dan he raised this as something to think about which I found intriguing. Put someone in armor on a battlefield cutting all day long - using external methods vs. internal methods who would get exhausted first? Fatigue makes cowards of us all.