This is just the effect of the lowest quality First Grade Integration Elixir. If there were enough of the highest quality Ninth Grade Integration Elixirs...

In each of the Seven Sacred Grounds, there are eight to nine hundred thousand, or even over a million, Integration stage cultivators.

The Seven Sacred Grounds are not lacking in late Divine Transformation stage cultivators in Great Perfection, but they do lack Integration stage cultivators.

Among the vast number of Integration stage cultivators, a small portion will inevitably cultivate to the Tribulation Crossing Supreme stage.