Roger and Shanks unironically are different than Mihawk and Ryuma because, first, they have never been addressed as dai-kengou in this story (Zoro doesn't dream of becoming the strongest swordsman per se but the strongest dai-kengou, an important nuance often ignored by translators and a fandom that only relies on translations instead of original content); and second, they don't aim at duelling their way to the top of the field of swordsmanship (which is exactly what Ryuma, Mihawk and Zoro had in common and what is likely involved in turning your sword black since it's a common Japanese trop).
The amount of canon information in this manga supporting that this issue isn't as simple as "carries a sword = swordsman" is undeniable, but people here, let's say simple readers, don't want to accept it since their vision is easier and more comfortable.
The amount of canon information in this manga supporting that this issue isn't as simple as "carries a sword = swordsman" is undeniable, but people here, let's say simple readers, don't want to accept it since their vision is easier and more comfortable.
Mihawk has been addressed as 世界最強の剣士 = Sekai Saikyō no Kenshi and 大剣豪 = Dai-Kengou: great swordsman
Zoro wants to become the strongest/greatest swordsman.