Mystery? How can One Piece be better than Naruto regarding mystery when Oda refuses to reveal any mysteries. Naruto has no mysteries because it doesn't need to rely on mysteries to keep it entertaining whereas One Piece relies heavily on these mysteries and Oda keeps introducing new mysteries 1000+ chapters into his story without resolving any of the past mysteries.
Supporting characters? You mean the strawhats that haven't done anything for hundreds of chapters? Or the Scabbards? Not sure how One Piece has better supporting characters. Naruto supporting characters where Jiraya, Yamato, Shikamaru, Tsunade, Guy, and much more not sure how Nami, Usopp, Franky, Brook, Robin, Chopper are better than them.