Yes, societies that placed a higher monetary value on slaves almost certainly treated them better.

Slavery is bad, but not all forms of it are equally bad. We have to acknowledge that because there's a whole spectrum of coerced labor between "literally in chains" and "my employer paid for school and I can't afford to leave."

Again, none of it is good, but it's important context.

No, but it adds important context

Why does humanity matter though?