I am so happy this morning! Goosbumps all over^^ I admit, the expositional revelation of the fruit's nature was somewhat off-putting, but that is for the Gorosei alone. And I feel slightly blue that the old theory of Blackbeard wanting the most powerful zoan (Kaido's fruit), is probably in the gutters now. I had a feeling that the resin theory flying around last two weeks was a red herring by Oda, and I am grad that that was the case.
Now to Luffy himself. It certainly does not seem like some other entity has possession over him, as many people were fearing. You cannot blame Oda for using the inherited will concept, that is the entire tenet of the story. And besides, in this case, Joyboy had this ridiculous fruit some 800 years ago, and he came to be known by the name Nika (also to Zunisha), and Luffy just happened to eat the same fruit. The Gorosei are terrified because of the precedent that Joyboy set at that time and probably because Luffy's character matches that of Joyboy's.
One Piece has a knack of picking me up even in my worst weeks and I am sure for many others, it is the same. My part in the One Piece fandom is about the only sense of belonging I have ever had. I am glad I discovered this story all those years ago. It is pure poetry.