Good board scores help, but alone they're not sufficient to overcome the GMO advantage. Returning GMOs, by virtue of having a pulse, are simply eligible for many more points than interns. They have points for a completed internship, completion of Step 3, and of course for the GMO tour itself. The system is not set up to permit outstanding interns to get a position over a GMO.
The only way an intern will get the nod over a GMO is if (a) the service has mandated that a certain number of residency slots will go to interns, or (b) there's an extraordinary perfect storm of prior service, grades, board scores, & multiple peer-reviewed publications favoring the intern and a weak GMO.
(a) is happening, to a limited degree, in some specialties.