All 3 are swordsman. Roger isn't weaker than Mihawk because he didn't forge a black blade, I don't believe that at all because Oda has never treated Mihawk with the grace required for someone of that stature, we saw it with Oldbeard, Roger speaks for himself, and now we are seeing it with Xebec. This is where Mihawk's title as the strongest swordsman comes in, he took swordsmanship to the apex. Only Ryuma has done this before him. Black blade is not a sign of a superior combatant but a superior swordsman. It is this until further notice.