Without Enma, Zoro's haki would not be were it currently is. That is a fact. While he worked very hard to master Enma and should be praised for it, if he was a battle genius like you claim he wouldn't have needed a "training tool" to help him unlock ACoC.
Zoro would have unlocked it eventually but it was a huge shortcut for him.
Without Enma I doubt he would have defeated King
Everyone needed their training tool for advanced haki.
Katakuri was Luffy's "training tool" for FS, observed and fought it for idk 12 hours?
Hyogoro taught his advanced armament (which infact facilitates for advanced conqueror's)
Zoro's natural talent is up there with Luffy's.
He learned how to cut steel mid fight, breath of all things. Learned how to do flying slashes on his own. Demonstrates a never before seen variant of conqueror's haki in Asura. etc.
Obviously yeah, King folds Zoro if he didn't have Enma. No advanced conqueror's = lose.
But then again, Oda could've randomly made Zoro that powerful like he did for Law and Kid lmao. At least I'm glad that Zoro had a more legit reason to be as powerful as he is now.