Qi Condensation. Foundation Establishment. Core Formation!
In the Lower Reaches, the gaps between those three stages were like enormous gorges that separated the cultivators into groups. With the exception of some extreme circumstances, someone in a higher stage could easily crush anyone from a lower stage!
During Qi Condensation, cultivators absorbed the energy of heaven and earth and then transformed it into rivers and lakes. During Foundation Establishment, those rivers and lakes became spiritual seas, giving the cultivators such strength that Qi Condensation couldn't even compare to it!
Overall, that transformation wasn't so much an improvement in the quality of the power, just the sheer amount!
However, Core Formation was different!