Pretty much this and almost everyone I talked to after doing the DRK quests they have said their characters changed. For my character his friends have become more of an Anchor to help him get past all the nonsense npcs throw (which he finally admitted) at him sometimes he still defends the meek and punishes the wicked as per the motto of the DRK. Yet now he REALLY enjoy's punishing the wicked in a strange sense. I also do recall according to the quest journal the WOL wanted to deal justice as they see fit without anyone holding them back etc, I mean we all remember 2.55 right? I mean come on most your characters must of felt like rubbish after being so powerless to do anything while villians bend and hide behind the law and politics to cause suffering.
We did nothing in 2.55 because we are the WOL we must use "politics" and follow the "law" because what would people think of us? They look up to us etc. Lore wise DRK do not care for that kind of stuff hence why "Fray" appealed to your character so much won't say why because of spoiler reasons. In the end DRK don't care for the law, politics or people using faith as a shield they will find you and end you no matter the cost, if you are committing acts of injustice and evil they will be there to kill you hence them looking towards dark power since its pretty much them against the world. No one will thank you, they will even hate you because the common man believes the word's of their leaders and soldiers etc and it does not help you that you are using dark/demonic powers while saving them as well. So even the people you saved may not trust you after having a glimpse under the mask.
It's the reason why I adore the DRK questline so much after being through all of it can the WOL simply put that "mask" on again and not change? Or leaving behind the mask completely? Or Perhaps just wear a piece of it?
Oh and possibly the DRK power source might be the same as BLM who uses the void because during the DRK quest line they say we use the power of the "abyss" and I assume its another word for the void just like how monk's instead of calling their power aether they call it chakra.