The way it looks to me, the nature of the battlefield really has changed, hasn’t it? For millennia it literally didn’t matter how smart a guy was—you just sent him forward with the line as part of a brute force attack and they were mere chum, so it almost didn’t matter whether he got mowed down or how many went down with him. But by the time Vietnam came around, operations were far more complex and multi-faceted, which required a minimum level of intellectual capacity not needed during the Crusades (which used children!), for instance, and could lead to the failures you describe. Today, of course, there is no real battlefield as in the type imagined during the Charge of the Light Brigade. If there that kind of hand-to-hand engagement anymore, it’s more street to street, building to building, trench to trench, hill to hill, tree to tree, etc, which also requires a higher minimum of intellectual capacity to execute properly than chivalrous open field combat.
Am I close?