its not a rumor
its not people say
its definitive . so at this point you would have to ask yourself why the author labeled mihawk the strongest swordsman and not shanks with the latter and him having many duels over the years.
if we don’t have bulletproof evidence nothing is definitive.
even if inside the story someone has a title it doesn’t mean that title can’t be fought and denied or explained.
there is also a reason why Oda chose Roger to be the main pirate of his gen, to allow WB to have his own gen only after Roger death and long disease, to have Roger beat WB captain. The PK was Roger, the one tied with the straw hat was Roger, the dream of the MC is Roger. And there is also a reason why when they fought no one won (and Roger was already a bit sick). And Oda also wrote everyone admiring or respecting Roger (Chinjao etc).
Same for Mihawk and Shanks : ODA chose to made them rival, to make Mohawk never officially defeat Shanks, to make them not fight for 12 years now, to make Shanks the role model of Luffy and Mihawk the role model of Luffy’s nakama and whatever we can say Luffy is the captain and the MC, to make Shanks the successor of Roger and the one Roger gave his hat and the straw hat is the most or one of the most important things. Oda also make COC the most mysterious and rarest and powerful power, and Shanks for now embodies that power.
You said Oda chose to say things but he also chose to say and show a lot of other things that made the lines blurry
matching the title holder doesnt make you the title holder rayan
no such thing as co title holders for obvious reasons.
if the title holder has fought and has never beaten the other strongest of his field the guy can be called whatever he wants he is not the strongest.
You can also see that the World something seek fights a lot : Mihawk seeks other swordsmen, Kaido seeks fights too. While Shanks or BM couldn’t care less. They want to be strong they are and they can fight you no problem, but they won’t seek you across the world just to fight you without purpose.