This is a matter of using an extreme example to showcase the point he just made.
Jessup isn't literally implying that only the president ranks above him. He's stating that he wants a woman in a superior position, and to support his statement, he then uses the example of the most superior position to him.
This is a variation on Godwin's law, which essentially means that when someone talks about a bad action/person, they use the most extreme example of bad actions/people they can think of (the nazis/Hitler).
Similarly, Jessup is talking about superior positions and therefore uses the most extreme example of a superior position to him he can think of.
On an unrelated subjective level, you may read into this that Jessup is being sexist and indirectly excluding women from holding a miltary position superior to him. By elimination, that would mean a woman can only outrank him if she were an elected official, of which the President is the prime example. However, I can't find any explicit confirmation on Jessup's ideas on women in the military, or military high ranking positions.
It's just as possible that he simply referred to the office of the president as a matter of extreme example (the most superior position) without implying anything about women in military positions.