Debates about Klaus's punishment of the six patriarchs were being held by billions long before he even left the battlefield with his people.
Many expected him to sentence them to death since their crimes really demanded such a harsh punishment. However, he never went that far. Rather, he left them alive but in the worst state possible.
Aside from the five patriarchs who still had their cultivation bases and some of the warriors who survived against Asmodeus and the chaos beasts, everyone else had returned to the True Immortal stage.
That was perhaps far more wicked than even killing them. Living forever with no chance to reach the peak was just too humiliating and painful.
Maybe Klaus wanted them to suffer every single day whenever thoughts of when they were at their peak came to mind. He wanted the pain to last forever, and so he was happy.
