Doflamingo is as sly as they come, a master of illusions who crafted his legacy using an anonymous identity as Joker
He is far more accomplished than Katakuri naturally, but this level of intellect and deception is contradictory to a true conqueror.
Neither are deserving, but Katakuri is a more fitting conqueror seeing how big of a champion he was in the eyes of his family, and how he stood firm against an opponent like Luffy and refused to win the fight unfairly.