The Secretary of Defense shall ensure that the qualifications of officers assigned to joint duty assignments are such that—
((1)) officers who are serving on, or have served on, the Joint Staff are expected, as a group, to be promoted to the next higher grade at a rate not less than the rate for officers of the same armed force in the same grade and competitive category who are serving on, or have served on, the headquarters staff of their armed force; and
((2)) officers in the grade of major (or in the case of the Navy, lieutenant commander) or above who have been designated as a joint qualified officer are expected, as a group, to be promoted to the next higher grade at a rate not less than the rate for all officers of the same armed force in the same grade and competitive category.