I think he should not be overlooking Santiago, in fact that's what I read from Nonito, he wanted to win this fight first before they talk about who's next for him. In the face-off, Donaire is the taller guy so that is a plus for him.
Having height advantage throughout his career, we have seen him knocking people out from Darchy to Ouballi before his reign was cut by Inoue. But now Donaire wanted to proved again that he can become a champion. So this is a step for him before we talk about him fighting for undisputed next.
Nonito was most taller, So he get more range as compared to other people.The shorter boxer will be easy for the Nonito, he can crush the short boxer using his hand power.In addition he had a power punch compared to the Santiago.Santiago had win many old experience boxer using his power arm.This fight will against the two power arm fighter.So the game winner will be the maximum punch player.The Nonito should win the game against the Santiago to prove his power against the most powerful player.This will make them to prove his power and make other to think about the match, even this help the Nonito to get the championship.