Evil, defined as taking pleasure in someone else's unwanted pain, exists. And if we pretend it doesn't and look for other motives when evil was the driving force we get a mismatch between map and territory.

Yes, but from the inside, one's utility function often feels like The Way The World Should Be. An evil person by your definition could still feel like they're Doing The Right Thing when they're decreasing others' utility. So I feel like nothing has really changed with regard to whether "evil" defined as seeing The Way The World Should Be and opposing it makes any sense.