Diminishing returns
The first time Nero saw a berserker, it was a huge shock. The first time he fought a berserker, he couldn't hurt it at all. If it weren't for a few tricks he'd prepared for with Jackal, even killing one would have been a hassle.
Of course, since then, he'd been briefed by the army and knew their strengths and weaknesses. A couple of Thunderous Claps is all it would take to bring this bulky monstrosity down. But Nero had a sneaking suspicion that he no longer even needed to do that.
Since his flame had been upgraded, fighting against the cursed energy coursing through this monster's body was easier than ever. Of course, Nero did not intend on wasting time trying to discover the limits of his ability.
He wanted to kill the berserker as quickly as possible and use Radix Augmentation on it.