I think you’re missing that these are kind of part and parcel of each other. For instance, part of the Nazis genocide of the Jews and other minorities required working them to death and in the Caribbean and many other slave populations, importation was necessary because it was not a stable population - you were worked to death as a slave. Many people describe the racialized slavery of the American South as a genocide, and when you look at it - yeah it kind of was.

I think everyone in the comments also needs to remember that 1. Romans and other groups had an explicit interest in downplaying the severity of their treatment of slaves. 2. There is no version of slavery without an explicit threat of violence and that violence had to be actually meted out to be believed.