Oda is a hack for drawing those "green" flames and haki coming off his blades so early in the fight.
The only thing to deduce from this is Lucci didn't give an opening to end things fast so Zoro dialed his haki back. I mean it's no shocker Zoro does serious damage even prior to green flames and CoC. So the issue was never dealing damage but landing it.
But the issue is this chapter he treated Lucci like a toy, thanks to Sanji's provocation, made it seem like avoiding Lucci and landing was super easy for him....so what gives?
Man Oda fell tf off with fights, he was never elite to begin with but he's all time bad rn.
There are a couple of things going on here. First, if you look closely at the width of the blade and compare it with the size of the haki, the haki is almost nothing. Its even smaller than the CoA leak here =>
It almost seems like Oda thinks Zoro has a huge haki reserve to the point he leaks haki unintentionally. This could be a common trend for top tier swordsmen as we have seen Oden could wield Enma like a feather.
Second, as I have said before, Oda just didnt want Zoro to interfere between Luffy vs Kizaru&Gorosei. So he just kept him busy with Lucci. In Oda's story, a birdcage can keep Zoro and an admiral away from Doflamingo. Using Lucci to keep Zoro away is a better writing compared to birdcage lol.