I believe he is a competitive applicant in terms of overall test scores, GPA and course rigor. I see how much he has put into his extracurricular interests for the past 4 years and I can agree that he is genuine but not a fantastic writer. His recommendations are probably decent but did teachers say he was the best student they have ever seen??? Yikes. I have to say after reading through several results threads for highly selective schools and looking at sample past essays, CC has done nothing for my confidence on an acceptance outcome! I can only hope HE doesn’t come onto the CC site as it would make the next 6-7 weeks seem like years.
Be sure he gets going on his other applications. If he isn’t accepted, it can really take the wind out of his sails regarding finishing his other apps. And it can remind him what he likes about his other schools, so in case he isn’t admitted to Duke, it softens that a little. 
He has completed 2 other applications including to his second choice school which happens to be our state flagship University. He also completed an EA application. He is giving himself a break for a couple of weeks before he starts on others.