I get the feeling the original idea they wanted was "black people benefited from slavery because they became Christian." -- but, this was probably too obviously a violation of separation and racist.

Black people didn't just passively learn Christianity, btw. We re-invented it into a theology of liberation that drove the Civl Rights movement. So much synthesis and invention occurred *despite* slavery not because of it.

So much of what those people knew has been lost forever, but not all of it.