Luffy is not chosen One.
He made his way where he is, and its because of who he became that he is on prophecys as a possible person to be the one to make things diferent. If he chose to be a lazy fuck he wouldnt be NOTHING.
Its about his OWN choices and actions that made him the candidate of be the needed person. Luffy is a genious in combat and has the Will and personality of great legends.
Its not about give him some aura, Power, demon , etc to make him stronger. He is what he is because of himself. And as a usuary master of his own fruit he can look better than other DF users with better druits since they arent near competent and strong as luffy.
As the sniper Dude from Black Beard Said, he thought DF users are nothing without their Power, not the case of luffy, ace and many others.
Luffy fruit Will NEVER be something special itself, the best you can hope is that some important person had It before. But that dont make the fruit special or Op by any means.