Simply put, I have no idea. We've seen almost nothing of Nero after acquiring his DT and beating a weakened Vergil is not a good metric for judgment.
All I can base myself on is his previous feats. We know that pre-Sin Dante suffered a crushing defeat against Urizen. And we know that Devil Breaker-equipped Nero did better than Dante against an even stronger Urizen (he was sitting - literally - on a whole month of blood suckage from the Qliphoth which made him more powerful than he was when Dante lost), being able to at least land a slash on him when Dante couldn't even do that with his DT and the Sparda sword.
So we have to start from the basis that Nero, equipped with his Breakers, is most probably stronger than Dante had ever been (which at the start of DMC5 and for the rest of the game till he gains his Sin DT is at least as strong as he was in DMC4). Let that sink in for a sec by the way.
Now, we all know that gaining Devil Trigger also boosts one's base power level, which in turn gets massively amplified when entering the demon form. The problem here is that in the case of Nero we don't have any good way of getting an idea of just how much of a power increase he got. All we know for certain is that currently, forget DMC1 or the anime, Nero can absolutely wipe the floor with DMC4 Dante (which by the current timeline is logically the strongest incarnation of him before DMC5). That in itself is impressive as hell but it's only a starting point for measuring his true power in his current state. We'll have to wait for other games or future media to show us significant feats.