I hope Oda ends up making Aramakis blades black if only so that Admiral fans can relax a little with a W. So far the portrayal of Greenbull shows no respect or preference for Swordsmanship,  so I heavily doubt that he has a feat shared only by Mihawk and Ryuma.
And yes it does matter if its a black blade because its been stated multiple times that black blades are both a swordmanship feat AND a straight weapon upgrade. 
A swordsman who makes a black blade basically garuntees a Zoro fight unless its an ally. And Greenbull will never.
	
		
	
	
		
			Wasn’t it Mihawk who said any sword could become a black blade? Lol
But you are contradicting yourself. Aokiji isn’t primarily a fist fighter, but apparently him achieving prime Garp punching power doesn’t devalue prime Garp. But Ryokugyu achieving a black blade would devalue Mihawk? Pretty blatantly contradictory.
		
		
	 
 Ryokugu isnt a sword autist like Mihawk, Ryuma or Oden. It's like some shitter who takes up swords as a hobby making a blackblade.
Garps training was specifically for fist punching. Unless Ryokogu has a Mihawk/Ryuma level master (or the drive Zoro has), yes it would devalue it.
They arent contradictory, they're nuanced.