There's been a lot of talk about Luffy being the "chosen one", since the latest discoveries of the Hito Hito no Mi, Model: Nika. That's fair, but it's important remembering that strong devil fruits don't make people strong in One Piece.
Having a powerful devil fruit is, of course, a significant advantage. When we look at the series' strongest devil fruit users, they usually have the strongest devil fruits (Kaido, Akainu, Big Mom, Fujitora, etc.) One Piece, on the other hand, does not approach it as though the devil fruits have made them powerful. "They're powerful, thus they have strong devil fruits," rather than "they're strong, so they have strong devil fruits." It may sound counterintuitive, but Oda has made a crucial distinction in his storytelling. In One Piece, strength comes from character, and characters have agency.
How does Oda accomplish this? Before introducing their devil fruits, he frequently introduces characters as powerful. Long before we see Crocodile manipulate sand, we know he's a formidable opponent. He is the head of a massive organisation that controls an entire country. We don't realise what his combat abilities are until we see his fruit later. Oda will frequently tell us how powerful someone is only by mentioning their title. How powerful did Aokiji appear when Robin told us he was an Admiral through chattering teeth? Strong character is prioritised over strong ability.
Oda ensures that his strong characters possess abilities that go beyond their devil fruit. Consider Akainu's tenacity and brutality. Fujitora's sense of justice, for example. Independent of their devil fruit powers, strong characters naturally rise above their fellows. As a result, rather than being "destined," their positions of power are earned.
Finally, Oda goes to great efforts to demonstrate how powerful you can be without the use of devil fruit.
Despite not possessing devil fruit abilities, characters like Shanks, Garp, Rayleigh, and Mihawk are top tier, but there are also characters like Sengoku, Kaido, and Big Mom who are insanely powerful before they obtain an ability. Even if they didn't have the devil fruits, they'd be significant players. In some ways, it's almost inevitable that these super-strong beings would attract super-strong skills.
These three factors, character-based strength, earned positions, and strength attracting powerful abilities, indicate that devil fruit users are not merely the product of their devil fruits, even if the strongest people have the strongest fruits.
Whitebeard is the best example of this. Although Whitebeard is said to have "the capacity to destroy the world," Oda makes it clear that he is more than just a powerful devil fruit. He’s a monster. He can outrun assassins and take dozens of cannons to the face while sleeping. He has a king's will and will go to any length to protect his family. He possesses a keen mind, a brave heart, and a deep, deep love. I can't believe he was born to be The World's Strongest Man only by eating the Guara Guara no Mi.
And I don't believe Luffy was meant to achieve his status simply by eating the Hito Hito no Mi, Model: Nika. Luffy possesses more than a legendary ability. Luffy he is, and he has always been Luffy. I believe he would have gained his rank whether he had any other ability or none at all. Nonetheless, Oda has created a world in which it makes natural that he would have a skill that is perfectly suited to his personality. Characters with precisely themed fruits abound in the One Piece universe!
Oda may one day explain why devil fruits behave in this manner. Perhaps he won't. To be honest, I don't believe he owes us an explanation. In any case, possessing a legendary ability isn't inexpensive for our future King of the Pirates. At least not yet.
Theory by Dddddddfried on opfanpage.com