Some have said that Philip is not power hungry or pointlessly sadistic and uh, that's not really true.
The point of the 'Witch-Hunter General' reveal is to show that he has selfish reasons for his genocidal actions. He wants to gain power and rewards for his efforts. Thinking it is what he is deserved. Wanting to be remembered as a grand hero.
Also...Well, there are many displays of the fact that deep down Philip....really enjoys hurting people. There is the Collector's statement of how he enjoys killing the Grimwalker's. Philip exposes the fact that Luz helped him meet the Collector in front of her friends just to hurt her, while grinning.
And of course, before he impales flapjack. He makes sure everyone, including Luz sees it. And mockingly saying 'You wouldn't want me to hurt your precious palisman would you?'
I would compare him to villains like Palpatine or Aldrich but he's more...self righteous
Palpatine or Aldrich would torture you to death for fun. They know what they are and make no illusions to themself they are anything but evil. Philip would torture you to death for fun but create a self justification that made him feel not only guiltless, but heroic for doing it. He's a serial killer with delusions of grandeur. But he does not just want power or to hurt people. He wants to feel like the hero as he does them.