In movies, does it really? The ending of Superman II implied that the Phantom Zone villains were killed (though there was a deleted scene of them being carted away by the police). Superman killed Nuclear Man in Superman IV (though that had the usual fictional copout that killing artificial life forms somehow doesn't count even if they're fully sentient). Of course there's the ending of Man of Steel, and Steppenwolf dies in both versions of Justice League, with Superman participating in the events that lead to his death.
Like I said, the "villain dies" trope is so baked into movie storytelling that it's common even in movies about superheroes who never kill in the comics. The new Supergirl is just one more example of that far too common practice.
But again, that's far less the case in the movies. Burton's Batman killed routinely. Schumacher's Batman was generally less lethal, but deliberately took the action that caused Two-Face's death. Nolan's Bruce Wayne was inconsistently portrayed; in Begins, immediately after he refused to execute a defenseless man, he started a fight that blew up the Assassins' base and probably killed many of them, and then there was "I don't have to save you" at the end. And so on.
I don't think a zero-sum solution like that is very heroic. At least, it's not superheroic, because the "super" means transcending the expected limits. This feels like the exact same situation as the Man of Steel ending -- the "hero" just letting the villain win the philosophical battle by sinking to his level, rather than transcending it by finding a better way. That is unworthy of the S symbol.