Wasn't this obvious though? Like Zoro said mastering Enma is him only cutting that tree once if he only wants to cut the tree and not cutting cliffs all the time.
Thats all that was stated about what Zoro was suppose to do from the get go. He wasn't learning some super slash ability. The sword already forces people to do super slashes. Literal fodder could just touch the sword and bam they do a super slash.
Zoro as a master swordsman is the one who stops the sword from doig a super slash and that's what proves he is better than those fodder swordsmen, he can actually make it not do excessive damage.
That's actually that was stated Zoro was doing and had to do.
And you are right, the haki draining only existed for Zoro to get haki training but I don't see how that's "cheap". I mean Luffy gets mid battle flashbacks and runs into haki experts willing to train and people always cry out that this is plot convenience. Then Oda changes it up with mystical items being used for training a la Dragon ball's hyperbolic chamber and THATS also cheap. Now what is Oda to do? Should he plain not have the characters grow?
Yo, it was more of a more emotional first impression post anyway.
The thing is, I know all of that, but coupled with that "only blade able to cut Kaido" hype the whole package came off differently. This way I didn't think of its haki draining ability as a mere PU tool, even tho, like I said, it's not like I dislike the idea entirely or I disliked those Enma scenes.
In hindsight I was probably more disappointed or rather confused about that blunt empty hype. Its special ability is basically just there to power up Zoro, which is legit, where I agree with you btw, but that's still something that somewhat had to "sink in" and it got the better of me.