How is this even a question? Luffy is an emperor ever since the end of the WCI when people started viewing him as one and the "do not engage" rule enforced by the WG only solidified that position. Opinion of one butthurt loser is irrelevant. Just like Moriah might have not considered Kaido a Yonko because of his personal feelings and envy and because he got his ass kicked by him, that doesn't change the fact that the rest of the world + the highest authority in the WG considers him one, and that he is just a pathetic loser.