Shusui saved his sorry ass countless times. If Mihawk actually defeated the man who held Yoru then that's a bigger feat that shading the sword. Defeating Real Ryuma and taking the sword of his corps is a greater feat than shading it.
Zoro DID NOT defeat the real Ryuma and there is no known swordsman who has defeated a person who made a black blade as of yet so your entire argument is pure head canon
Ryuma is undefeated and Mihawk is currently the strongest swordsman so there is no mention at all that a person who can't make a black blade has beaten A person who has. I'm not going to suddenly take your random power scaling statement as if they are facts in the story.
You want to downplay making black blades as a feat even though this is the rarest feat ever accomplished in the series. If it's not a big deal then why hasnt everybody been doing it? It's not a big deal yet the pirate king, Oden, rayleigh, shanks never pulled off this "not a big deal" feat.