And, if you believe that pure leadership is how one rises to become a flag officer, you're definitely kidding yourself. In the modern era (that is, since the adoption of DOPMA in the early 1970s), one can no longer be a complete incompetent and make it to general or admiral. However, some of the politics that go into the designation of who is even eligible for that grade are so hidden to civilians that their bias is not readily apparent. For example, of all the generals in the Air Force less than twenty are not rated officers (pilots and navigators)—and most of them are doctors. This bias is built into the system, because Congress in its infinite wisdom has determined that nonrated officers may not command units that have any flying mission—or sit in the chain of command above them. However, most pilots do not begin to have any real supervisory authority over enlisted personnel until they become majors (10–12 years down the road), which to say the least causes those of us who did some real problems. Enlisted personnel are, even in the top-heavy Air Force, 80% of the troops.
It's no longer quite the case of getting promoted to general on family-tie grounds. However, the need for well-placed mentors is even greater than in "traditional" politics, for a very simple reason: "grass-roots campaigning" is insubordination, not building a power base.