It's not.. It literally says Sekai '' Saikyou '' no Kenshi.. World Strongest Swordsman.. And Zoro's dream is Sekai Ichi '' Tsuyoi(strong) ''..
They are 2 different titles.. Like Yonkou and Great Pirate..
You're all over the place on this..
They are completely different wordings.. Daikengou is Grandmaster Swordsman.. Saikyo literally means '' Strongest '', Mihawk's introductory box is '' Sekai Saikyo(Strongest) no Kenshi ''.. And it's not '' Sekai ichi no kengo '', it's '' Sekai ichi Tsuyoi(strong) no Kengou
Grandmaster Swordsman doesn't equate to Greatest Swordsman and it's not even greatest.. Saikyo doesn't translate to greatest, it translates to Strongest, you can do a quick search on the internet for that, it's a lie..
You are using google translate logic, when someone say this swordsman is the best at swordsmanship, they say greatest swordsman, it might be different in Japanese, but in English its called greatest swordsman which all mean same thing.
I told you; there aren't 3 different titles. They are all same. You not being smart enough to not understand this is not my problem.
Not once in the series they use these titles separately, not even once. Either Zolo say ''sekai ichi no kengo, or ''saikyo kenshi'' or ''dai kengo'' not once they use it both or 3 at the same time. Because they are all the same.
Why you think they say in anime ''sekai saikyo kenshi'' but
why they translate in subtitles as ''greatest swordsman''?
Because you don't say strongest swordsman in English, thats saying like ''strongest marksman'' which sounds silly.
Thats why official VIZ first translated ''info box'' of Mihawk as WGS (when it says Saikyo Kenshi) which is correct translation,
But then ZKKfanboys cried, and they forced VIZ to use the wrong translation which is WSS.