Enma increases Zoro's haki output which allows his attacks to be much more powerful than what he can achieve without it.
Yoru would possibly do the same thing with Zoro until he his fully able to control it, and possibly to a much greater degree, considering it's already black.
Question is, would Zoro be able to control Yoru without first learning to master Enma, or would Yoru turn him into a husk.
I don’t know about that. I don’t think all great sword have the same gimmick as Enma. I don’t think Ace, Griffon, WB bisento, Shodai, Yoru etc all suck up your Baki and let you empty.
Just take Shusui, it’s a legendary sword, a second grade one like Enma, and it’s blacken. Yet it didnt suck Haki or life force.
All those great swords need to be mastered so I agree that Zoro can’t use Yoru before mastering it. But maybe the gimmick is different from each sword. Maybe for the Shodai it’s you have to take over the curse, maybe an other crush your mind etc etc.
I think Enma sucking and releasing ability is only for Enma.