I like the struggling Zoro who tries to overcome hmself than the boring Zoro who's just there to look cool.
Well this is a sword technique. Zoro learns sword techniques as fast as luffy does.
Remember when he was learning 36 pound phoenix? He pulled it off FIRST TIME with no hassle after just saying he'd never done it properly before.
You saw Zoro struggle with Enma once and that's the end of that. He's now completely fine.
Same way he is shown struggling with Sandai ONCE and he's fine forever.
And same way he struggles with shusui once and he's fine forever.
Si if Zoro is still having problem with Enma, it would mean he's not as good as he was pre time skip