There was a reason why there weren't so many Undead Stage cultivators in the Human Realm Upon Heavens. For the same reason, a level-two Undead Stage cultivator could easily crush a level-one Undead Stage cultivator. The difference was huge. It was like a thirty years old man crushing a one-month-old baby.
There was a good example.
If reaching the first level of the Spirit Origin Stage needed one glass of water, then it took two glasses to reach the second level, and three glasses to the third level… Reaching the next stage needed two times of the water. Reaching the ninth level of the Spirit Origin Stage needed nine glasses then reaching the next stage needed eighteen glasses, not ten. To get one level higher, it required eighteen glasses of water… Thirty-six for the second level, fifty-four for the third…