Trading a sword, for a inferior one, when you are about to face a yonko? Buddy, you simply don't deserve to win. But oh well. If people wanna think this is good writing, be my guest.
And Enma is a magical sword.
Sandai had to be tamed.
Shuusui had to be tamed.
Enma is the only one that sucks Haki from the user on its own.
That's a magical weapon.
And Enma is a magical sword.
Sandai had to be tamed.
Shuusui had to be tamed.
Enma is the only one that sucks Haki from the user on its own.
That's a magical weapon.

First, the trade to enma were between zoro and hiyori. Dunno why you threw hissy fit on the writing for 'Wano people'.
As the chapter explained, there was a hint that hiyori noticed the wado ichimonji and just believed that zoro would master the enma sword. Shushui is currently better than enma since it's already reached the black blade state. But well, oden still managed to give a scar to kaido so it's not like black blade is necessary to beat kaido