Enma is important because it stores Oden's memories and feelings and that's some dope stuff. This is why it's so hyped, it also reminded Kaido of the past time and he saw that through CoO.
However there's no evidence of Oden's soul standing in there, he should be gone, he ain't no Brook or something, that's just mental stretching.
And by the way when Oden died his arm was normal so he didn't store any haki inside Enma, that's Zoro's haki.
Also Enma cuts more than necessary in that it forces the user to use more haki than he would but Zoro seemed to learn how to control that and used this peculiarity to get stronger via training but now Enma is not cutting more than necessary because Zoro's arm is normal, the sword is not forcing something crazy out of him.