User blog comment:CNBA3/Armament Haki Confirmation./@comment-24850639-20160923132005

Two things: There's an Encylopedia of Devil Fruits, and it was a REALLY big deal that Vegapunk/Caesar made a breakthrough on artificial devil fruits. I don't think there'd be an encylopedia of them if there existed a way to constantly create them at a high rate, and of course well, why are Caesar's fruits "artificial" then? Devil Fruits could have existed since the beginning of time for all we know. I'm a big fan of the theory that they all come from one big tree, and through some kind of big incident ended up getting distributed throughout the world. That doesn't really matter for your question though, in either case I think your logic is solid. In addition to that, it wouldn't really make sense for a DF to be a prerequisite to being the strongest, or just incredibly powerful period. Shanks, Mihawk, Garp, Rayleigh, and Zoro are just a few examples of proof that you don't need one to go toe-to-toe with the best of them. I don't think Oda introduced haki simply as a means to counter DFs, I think he has a much deeper purpose with what it means and how you develop it. Rayleigh told Luffy that he can't train his Haoshoku, he develops it by developing himself as a person. We still don't really know what it means, but at the very least Oda's left haki in general open-ended enough that we're still dying to see how people like Shanks earned their titles.