Controlling a sword means you bend it to your will.
Zoro did it against a powerful sword like Enma by unlocking CoC (consciously).
Mihawk controls the strongest sword in the world, what do you think that says about his conquering ability?
Also, Zoro literally acknowledges that becoming the world's strongest swordsman is a kingly ambition of one who has CoC
This isn't even foreshadowing, Oda is blatantly telling you that.