What if we already seen pluton in onepiece in the fishman island arc? what if luffy already broke half of it? yes I believe pluton could be the biggest ship in the world the Noah. the Noah was left by joy Boy and by leaving it there he left it with the most trust worthy hands he knew and the key to unlocking the true power of pluton posedian. by leaving it here it makes more sense why he cared so much about it like imagine you make plans to destroy the red line and then u figure out your going to have an early death would you not leave the last of your power with the other person that knows of these three powers and her descendant will be the next to carry one of these powers and leave it for the next generation of powers