Dude isn’t into despair as a principle. Senpai is a sadist who enjoys SEEING despair. It’s a major weakness as you note, but that’s what the origin cause wants demons to be like.Isn't it better to see the faces of the park guests in despair?
Isn't it better to have the authorities looking for thousands of runaway criminals rather than having them know who is the mastermind and then focusing on you?
With leaders like this, they will be going to be stopped by a no magic human with plot armor at every turn