I can't read japanese so the way I see it is this:
1- If WSS is a true translation then Mihawk is the strongest swordsman regardless of your skill lvl (Kengo, Dai Kengo, etc...). Meaning he's stronger than Saint Shanks and all other swordsmen like Vista, Shiryu, etc...
2- If WGS is a true translation then Mihawk wields the best swordsmanship in the world. It's not a title related to strength. He could be the weakest swordsman ever as far as we know but still has the best swordsmanship in the world.
3- If WSDK(World strongest Dai Kego) is the true translation then Mihawk is only the strongest amongst the Great Swordsmasters/Dai Kengos in the world.

