I won't say plot armour since it don't look like Zoro has full control of the sword .
Seeing Zoro fully control the sword without getting tired after one attack is something we might see him do in battle.
So this could be the set up for that.
He missed because he tried hit an enemy running from him which is exactly what happened in chapter 1002. Zoro hit Queen's weapon when he's far away from him. X We have no reason to believe he'd miss a gigantic Dragon which is like 2 meters away from him.
Maybe Zoro simply can't control Enma as good as he should with proper mastering over it. The guy said he needed to unleash it more last chapter and now is panting and angry for missing after he tried a slash he maybe can't spam freely. Let's see what happens with this "no ordinary sword" thing.