OP Magazine mentioned that being the "strongest" is not that clear cut. Oda may consider Kaido the strongest based on his durability, and overall physicality, but one thing is clear, he is crap against swordsmen, and he has not faced a swordsman on the level of a Mihawk, with a black blade.
I kept Kaido as #1, and gave him the benefit of the doubt. But right now Mihawk is the strongest man in One Piece in 1 v. 1, until Blackbeard surpasses him.
??? Oden was about to slaughter him until they pulled cheap tricks, which Kaido apologized for.