This is a very interesting thought: the Dowdy alien you mention has wiped out an entire race of 50 billion beings, but is aware of his crime and lives in self exile. He’s committed an atrocious crime in a rage fit.
On the other hand, the changelings committed a planned crime with intent to cause suffering.
I’m not sure who’s worse: the Dowd by magnitude of the crime, but the Changelings ruthlessly command their Dominion.