See the problem is that Kozaburo, Enma’s creator, only said one thing about Enma, and then Zoro IMMEDIATELY does the One thing Kozaburo says.
we aren’t led to believe that Zoro half accomplished what Kozaburo said, not he just did the thing Kozaburo said he should do. And that was that
the only argument you can make is that Zoro himself said that Oden did the thing easier than him. As in Zoro thinks Oden did the thing Kozaburo said to do, more easily than Zoro was doing it
So if there is something more to Enma it’s Zoro just ASSUMING that he should do whatever he did already but easier because of Oden.
Also everything else you thought about the mechanics of other swords was addressed by Kozaburo too. Kozaburo says that some just have “stronger personalities” than other swords… for no reason… It’s just random luck… Remember that Kozaburo also made Zoro’s Wado Ichimonji, and it has no Enma type powers.
So Oda’s explanation for Enma’s Haki suck, and Sandai being cursed and Wado Ichimonji being normal is that well, they just have different personalities, and the way you can’t explain why humans have different personalities, you also can’t explain why sword do too.
It’s a classic Oda “who cares” answer