Boruto: Kishimoto Has Already Explained How Sasuke Uchiha Surpassed Naruto Uzumaki

Kishimoto: Sasuke has overtaken Naruto in Boruto. He trained through the timeskip, kept Eternal Mangekyo power and even wounded Code — while Naruto was sealed in Daikokuten. Naruto might catch up when he returns (Ch.30 Jan 20).