The point of the scene is to show how the sword needs to be tamed otherwise it will be a hinderance that will absorb the user's haki more than the user actually wants to give.
This is forcing Zoro to train his haki in order to be able to use Enma.
Enma was initially a downgrade as Zoro couldn't control it. (A master swordsman should be able to cut anything he wants and not cut anything he wants, Enma made this impossible)
However, after Zoro gets better Haki control, Enma will be as useful as Shusui.
Shusui is the national treasure of a country full of swordsmen. Enma on the other hand isn't even more special than the other sword Oden had.
Enma has the haki buff thing and Nidai has the curse thing which could be harnessed as a power up in the right hand. I think they are equal. If you make either Black then they become Supreme Grade weapons and they will still have their "magical" abilities.
Those extra abilities make them slightly superior swords to Wado. And if they become black they will be better swords than Shusui.
It all depends on just how 'cursed' the Kitetsu blades are...
If the biggest asspull in the story (Asura) had something to do with Zoro wielding the Sandai Kitetsu, then the Nidai is 100% better than even Enma