And why wasn't Rocks' the WSS of his era?
Because the title was created when mihawk singlehandedly went around the world to prove he is WSS
none of these titles existed before. Xebec wasn’t WSM or WSS or WSC. Because none of these titles existed back then. He also wasn’t pirate king since the term Pirate king was invented for Roger. The titles were created in SPECIFIC SITUATIONS.
WSC was created when the rumor that Kaido cannot lose in a 1v1 spread around the world. WSM was created when Whitebeard seemingly showed that he can singlehandedly end the world. (That’s why Whitebeard had the WSM title at the same time as Roger was pirate king and even at the same time as Imu was obviously around).
and Mihawk created the WSS title not simply by being The strongest swordsman, but by LITERALLY GOING AROUND THE WORLD TO PROVE IT. And yes, around the world includes Mariejois, Mihawk was a warlord, he has been to Mariejois. If he thought and Gorosei or Holy knight was stronger than him, he wouldn’t be WSS.
It's hard to tell what Mihawk thinks about the title since he rarely talks or mentions it
No he explicitly tells Zoro in Baratie that he’ll wait for him at the top of the world. Mihawk directly says he is the Top of all swordsmen. And this isn’t even Mihawk over inflating his position since in the same chapter he acknowledges that pirate king is a title above his own
and then later in Marineford Mihawk isn’t sure what the gap between him and WSM title is (although of course in this instance he’s thinking of the Prime WSM Whitebeard, he has no idea how much Whitebeard has deteriorated) So Mihawk is very fine with properly placing himself in the food chain of power. He’s not arrogant or delusional about his strength or anyone else’s strength. In that same arc, he’s fighting a weakling like Luffy and he soon realizes that actually Luffy has a power that already eclipses his own even in Marineford, the power to gather allies who are willing to die for his cause.
So not only does Mihawk legitimately think he is in fact the strongest swordsman across the entire one piece planet, he’s also incredibly conscious and humble about anyone being stronger than him and he seemingly doesn’t feel any which way about that.
Keep in mind that Whitbeard's WSM title was explained by saying that "he lived as the world's strongest man, so that's why he was one." And since nobody in the community cares I guess that's enough explanation.
In the manga the WSM title is associated with two feats. At first it was buggy saying that simply because Whitebeard could have an equal fight with Roger, that made him WSM. But then later on this feat isn’t even mentioned in Marineford and Sengoku only seems to care about the fact that he genuinely thinks Whitebeard can end the world.
and btw, this is a big deal type statement. I want to remind you that Imu cannot do this. Imu needs Vegapunk and decades of technology to replicate the mother flame and the ancient weapon Uranus, and 5 consecutive uses of Uranus to flood that world, AND THEN Imu would have managed to “end the world”. Supposedly Whitebeard can do a feat similar to this, BY HIMSELF.
And the vivre card says that Whitebeard’s was WSM before he even had that “equal fight with Roger” that we saw in the oden flashback (the fight that buggy was obviously exaggerating since it was entirely friendly). So I would say the Sengoku statement is more accurate about why Whitebeard is WSM. (But note that, Whitebeard’s title isn’t a 1v1 combat title like WSS and WSC in this case)