I think you overestimate too political and military leadership in saying If x are not useful then someone would have pulled the plug on that. SOF of WWII were borne out of circumstances but SOF of current incarnation was the result of political leaders wanting to fight potentially unpopular wars cheaply in term of body bags and popular backlash, plus it serves a good propaganda purpose to keep the public attention on something more political palatable than the sorry result of said war effort. Most of the missions in Iraq and afghan wars didn’t need any of the specialized training popularized by Hollywood and heavily promoted as part of the SOF image: night mission to kick open doors and shoot people dead, regular infantries are perfectly capable of forgoing a few nights of sleep to shoot at other people.