Luffy had a teacher in the form of Hegoro. Enma acted as Zoro's "teacher". Who taught him not to restrain his haki, but her "lessons" almost cost Zoro his life in a fight with King. And this is in your opinion "free"? I would understand you if Zoro could not release acoc without enma, but he has already shown how he covers all three blades with it and only Sandai. The only blade separately covered with haki-acoc at the moment is sandai kitetsu
You said that Kobi got it for free, I say that it's an exageration, and you say that Zoro didn't get it for free. Trolling aside, Zoro trains hard, Kobi trains hard, Luffy trains hard. Want to say that Zoro trains harder than everybody and has the biggest dick and pisses farther than them? Go ahead. But nowher is shown that anyone got their COC undeservingly.