The killers in this one were fine when you apply the notion they're psychotic & completely mentally unstable. We literally got an insane asylum in this movie lol
Sure the past killers weren't exactly sane, but their motives were mostly revenge driven. Except Jill & Amber/Richie who were fame driven so insanity was definitely a factor. Which is why I was surprised Jill didn't have a highly convenient cliché cameo at the mental institution.
Circling back to this movie's killers, it wouldn't feel so underwhelming for people if Stu had been the mastermind puppeteer all along. They'd just be pawns on his chess board.