The short version is that the premise is false. Now as a matter of history, you cannot assume that a slave system mirrors the U.S. slave system simply because its a slave system.
So, what was the difference between the two slave systems where Black people are concerned?
Its not a matter of justifying it or not, liking it or not...its a matter of getting the subject matter correct.
Specifically, what subject matter is not correct?
That is in addition to the conflation of the "Arab world" and "Muslim world".
But, isn't the "Arab world" and the "Muslim world" about as conflated as the two could possibly be?
" . . . we can't skip around or start with narratives, definitions that don't hold on any historical examination . . ."
Which narrative do not hole any historical examination?
What is being skipped around?
The "3 major religions" are treated as foreigners entering Africa when the exact opposite is the case.
What makes the "3 major religions" "foreign" is the fact that the concepts and consciousness and truths that were originally African have been deviated, rewritten, revised, taken away from and added to, swallowed wholly and then regurgitated back down the throats of Africans many centuries later, by force, enslavement, conquest, and conning. Centuries of War, Conquest and Turmoil waged against Africa wiped clean centuries of African knowledge, history and consciousness, creating a "Blank Slate" to write regurgitated, revised, and re-written, therefore, foreign, versions on the African psyche.
Its the same narrative re-writing that causes people to associate Rock n Roll as "white peoples music" despite the fact that Black people originated it.
I'm not sure if you are saying that African created slavery in the first place or if you are saying that slavery existed in Africa before the Arab or Trans-Atlantic Slave Trade. I know that historically ALL races of people have participated in slavery at one point in their history or another, staying on the point of Africa and African/Black people, it was only Africans/Black people that have suffered the most brutal, far reaching, defeating, exploitative, genocidal system of enslavement that went as far as to make slavery racial and to create a slavery system base purely on race and/or color, which still exists today in some Arab countries.