Narcissists are absolutely a thing, but it sounds like you're conflating two groups.

The poly relationships I know, and the open relationships I know, just aren't even close to what you're describing. Even the closest singular example to what you're describing — one out of a dozen people who are open about being poly and a dozen more who are open about being open — was, despite being extremely selfish, not sadistic as the person you describe appears to be.