That was my point there were no competitors for WSM & WSC or even Yonko per say it just happen and that is how the story set it up .
But the story did set up WSS as a title you can go directly after problem was that most people in story don't use swords alone.
So Zoro have to get stronger fight differnt people than pure swordsmen before he fights Mihawk .
Oda was never going to do there is a pure swordsman on every crew for Zoro to fight
There is no such thing as "pure swordsman" tbh.
There are swordsmen who use DF abilities like Brook or Fujitora or even Kaku.
Then there are swordsmen who use Haki abilities like Vista, Scabbards, Zoro, Shanks & Mihawk.
WSS is simply the strongest swordsman, you don't have to beat every swordsman in the sea to be called the strongest, you have to beat the current strongest and then you will be known as the next one.
Meanwhile, you gotta beat every pirate in the sea in the race to become the Pirate King.
I'm sure one or two rival swordsmen for Zoro would be nice, no doubt.
But his ambition doesn't work the same way as Luffy's does.
No point in using the metric for the Pirate King title or Yonko title or Shichibukai title & comparing it to the titles of Worlds Strongest.
No the WSC is about the strongest creature which is the beast Kaido.
The WSM is about the man who is currently the strongest person alive based on overall strength.
The WSS is about the person who is the strongest and has the most skill with the blade.
Anyone could theoretically challenge for each of these titles. Most people are challenging for the WSM title unconsciously probably.
WSS title is the exact same as the WSC title or WSM title.
It's the
Strongest Swordsman.
Meaning in a fight between two Swordsman - Mihawk will always win.