So a slash that was intended to simply cut a tree ended up slicing the coast?... That AP boost is absolutely ludicrous. No doubt about it, Zoro's easily G4 level with such a monster sword.
Considering the angle of the slash, you might not even be able to tell its full power as it cut cleanly through the coast and got eaten by the sea.
But it's similar to G4 with its drawbacks too. In order to obtain such a crazy AP boost, Enma sucks away Zoro's haki against his will. Knowing Zoro, he'll be able to control Enma soon so he would be able to regulate exactly how much haki gets used up in each attack, instead of having to replenish afterwards. But using that much haki would bring on the same drawbacks that G4 does for Luffy, i.e. Enma's power is limited, but easier to control than Luffy's G4 forms.
Anyways, it's good that this is a power up that's been earned by Zoro and one which requires a set skill level to even be able to safely use. Unlike a certain straw hat who got handed his power up by daddy out of pity which was an all-round stat booster which specialises in hiding and cheap shotting with no drawbacks except from the shame of acknowledging his own weakness.