As I said, either people don't read half of the manga when it comes to mihawk fanboyism, or they are simply trolling.
Killer's intelligence is
above average when it comes general knowledge about the marines and the pirates. There is no reason to doubt Killer, because he knows better than you. Killer > your mihawk fanboyism.
Marco also knows better, which is why he sent Vista alone to solo Mihawk, and he did it with ease.
And every single title, is what people say. There is no such a thing as ''E.Oda informing us from outside of the manga'', mihawk's shitty sword title showed up only after Zeff told us he is the most famous swordsman, but it doesn't mean he will win every fight in a sword fight, because there is no such a stupid thing as that, Vista is the proof of it, Wano Samurai are the proof of it, because mihawk never beat Wano Samurai as well. Zoro novel is proof of it.
Zoro Novel: ''One marine claims that the strongest swordsman in the world is definitely Mihawk, the other marine claims it's Zoro. They witnessed their sword techniques in marineford and dressrosa. Mihawk cut down gigantic ice block. Zoro cut down gigantic Pica. They start talking about other candidates: Vista, Shanks and Ryuuma. A marine says Vista was able to fight Mihawk equally for a short moment. Ryuma is strong, but he is already dead. According to another marine, Shanks is said to be the rival of Mihawk. He faced Akainu without fear. 2 of the marines have heard that Shanks is a very strong swordsman. But another marine says it's not that Shanks showed his great technique with his sword in Marineford.''
--- Translation by Sandman