After repeatedly slamming my head into a wall in order to acquire the necessary mental ability required for height scaling, I checked my newly acquired notes for height scaling and noticed that, according to the One Piece wiki, Linlin is 880 cm tall while Kaido is merely 710 cm tall.
This noticeable difference of over a metre in height, clearly shows that it was Big Mom, not Kaido, who was the World's Strongest Creature by a significant 170 cm margin.
Now excuse me while I go and consume the liquid contents of my antique thermometer which I am certain will further enlighten mineself in the art of height scaling.