The recovery speed of the Essence of Life was slower than Zheng Yichen had anticipated, it being possible to regain half of it in the previous world relied on the substantial boost provided by those Oath monsters, which, due to their confrontation with the Oath Beast, were already the apex beings of that world.
If Zheng Yichen hadn't decisively wiped them out, the natives of that world would have only felt despair when faced with that batch of Oath monsters.
After a day of battling in the Chaos Furnace, the result was that the Essence of Life he had recovered was not even half of what he had regained in the previous world.
The life force contained in the blood of the creatures here was strange, not unusable, but diluted, to be specific. It was like the Fervent Blood Life granted by the Eye Pupil of Life, which could be used as or substitute for life force, but when facing entities that extracted life force, the result would be akin to gnawing on air.