Zoro needed to go all out and master AdCoC just to use Enma...
Not really. Mastering advCoC was basically a side product.
Enma's effect is that it pulls a shitton of haki from the user, making them think they'll go out of it. By restraining his CoA in order to save it, he restrained enma's full potential. However, once the user gives the sword full access to their CoA, I think it doesn't just eat it all up - it just works properly like a well oiled machinery. This is proven by Oden who evidently was not capable of using advCoC.
When zoro awakened advCoC he was basically thinking 'alright fucker, here's all I got, eat it'.
in short - he wanted to fart very loud and he accidentally shat his pants