When will people learn Oda doesn't care about the titles? Strongest man was fake in marineford, he was so weak that Marco and Jozu needed to save him from several times. It should've been the opposite. Luffy saves the crew from Lucci, but ''WSM'' WB was in no position to save his crew.
Oda would never give a guarantee like that for Luffy's sidekick Zoro, he wouldn’t even give that guarantee for Luffy, who will be stronger than Zoro.
Oda also likes mystery, remember a character like Cracker doesn't even have his real face on his wanted poster, he was hiding his face and his real power. The government said Moria is dead when he was not, they also spread lies about many things. No one can give any guarantee on anything. As Kuma said, no fight is %100 guaranteed, he said no one thought Lucci would lose. Which is also why the Zoro novel states Vista might be the WSS not Mihawk, because there's no guarantee, Mihawk never beat the guy and asked for postponement. One thing is for sure, whoever reaches the Laugh Tale, will get the ultimate prize. People are not randomly running around and saying I am the strongest at this and I am the strongest at that, because its stupid. As Rayleigh said to Kizaru, the life is always full of surprises.