Cause and Conclusion
Any hopes of excelling against this new Shadow Disciple faded into nothingness as Dorian, Juno, Ivaar and Mephisto realized that their efforts to make Atreus submit to themselves had gone in vain as the latter not only beat all of them together as one but also trumped them in regards of battle strategy.
Kahn on the other end decided to use this approach of bullying them using his superior cheat skills because he wanted to break their will to fight and any ideas to cross him in the future. So they don't stand in his way now or ever.
He used the exact strategy he just cited.
First, he intentionally provoked them and goaded them into fighting all at once, making them reveal their hand while they were under the impression that Atreus was at their mercy during the battle.
Then he made them expend all of their world energy through attacks and skills while constantly evading and sometimes getting hit by their attacks.