It was considered common knowledge that fighting above your realm and killing such an opponent was almost impossible. Even a minor realm increase was no exception.
While there were geniuses that were able to contest against an opponent above their realm and fight evenly, almost none of them were able to defeat or kill those opponents. Defeating an opponent was ten times harder than fighting evenly against one.
As such, the final fight of the third trial was against an opponent a minor realm above each cultivator.
For cultivators at the peak of the Qi Condensation Realm, they would have to fight a half-step Core Formation beast, which was not quite Core Formation yet, but stronger than a late Qi Condensation expert.
Since John was in the Mid Qi Condensation Realm, he was situated against a late Qi Condensation beast.