I'm gonna keep it 100% with you ahill, I think you're actually a smart guy but you lack common sense. We've already explained to you why not everyone has a blade blade.
OK. Sorry to have exploded like that tho, I should try to remain more collected in instances like this. I'm under some stress with all this situation here and end up taking comments like this more sensitively than needed.
As for Mihawk's black blade, I've seen some ppl theorizing that such can be the result of Haoshoku Haki activation on it. It's said since the beginning of the journey (more like implied, I guess) that swords do have their own will, and that it's up to the sword to choose its master. Since Haoshoku is linked to one's will, it can be argued that the black tune the swords acquire can be a tangible manifestation of the swordsman imposing their will, completely, into the sword.
Ryuuma's sword is also naturally black, so he seemed to have attained a similar feat to Mihawk. I'd say this much more speaks to the level of mastery and "intimacy" the swordsman (that got it) have with their sword than necessarily a testament to their true fighting proficiency.
It's also possible that with succession usage of Armament Haki, the sword kinda took the "will" of its owner and acquired such black coloration, that's the color of Aramment Haki, similar to a child leaving their mom's thumb and gaining a life of their own... In a sense that, only then, the sword is awakened, let's put it that way.
I'd even say that Mihawk's sword could be black from the beginning, but Zoro's convo with that Fox-dude from Wano makes that unlikely, as he implied the acquiring of a coloration counts to the swordsman's skills, and not to the sword's from-inception trait. It's curious though that Zoro wished to question the man further, showing the subject seemed still up to him... so i question whether the black blade is something so simple as "subsequent usage of armament haki"... which would mean something easy for Zoro to piece together.
Still, Mihawk seemed to have WB as a superior force by the way he referred to him in Marineford and coupled that with he being still < Roger in his prime, make it pretty impossible to me to have Roger as below Mihawk. We also don't know if Roger's fighting style revolves entirely to swordsmanship, plus we don't know if he has had just one blade... maybe he has a lesser attachment to his material swords and discards them more often, not giving them enough time to absorb his Haoshoku's Haki or Armament Haki --- or whatever causes the black aspect in the swords.