The seniors are also simply candidates, so it would be believable to say that they don't always have the full picture. If the juniors actually perform better, I don't really see NASA shutting them down because of seniority. It isn't Japan after all, and Hibito did manage to hop to the moon.

Judging from how everything has been handled so far (Mutta's delay due to Hibito's illness, Hibito's desk job), HQ does all the deciding.