The US department of defense is the largest employer in the world, you have to have redundancies when you have nearly 3 million people working for you. An inde

The US department of defense is the largest employer in the world, you have to have redundancies when you have nearly 3 million people working for you. An independent intelligence service wouldn't have the interests of the other organizations it served. There are several independent intelligence services and military branches have their own. You want your intelligence service on your side and have separate services for separate missions so that priorities don't get mixed up and you don't have to get political to get what you need from some other organization. It's not a matter of "this is too complex" but picking your poison as to the drawbacks of several different org structures.