The demon hunters' appearance changed the tide on the battlefield.
Hao Ren realized that he had miscalculated something and that something made the battle more difficult to fight than he had expected. He did not expect the Malevolence in the shadowy realm to be so powerful and have so many qualities. It was harder to kill and was able to use its environment to its advantage. Hao Ren had misjudged the shadowy realm's "outsider-repellent" quality. He thought that since the Malevolence had split from Vivian, its close proximity to Vivian would curtail its power, but that was not the case. The Malevolence was not entirely separated from her "mother". She was still part of her. Not only would the realm accept that, but it would also strengthen them.
The misjudgment did not make the Malevolence invincible, but it had no doubt caused great trouble to Hao Ren.