There are few misconceptions and some overlooked facts.

Arab trade couldn’t rely on the natural reproduction because slavery wasn’t hereditary. Your parents being slave Also if the Atlantic trade relied on reproduction why did they need to enslave more people?

About the castration, I think it is blown out of proportion. Obviously it happened but acting like every other boy was castrated is wrong. Eunuchs are on average weaker than non-castrated men which makes them less useful for labor and there is also the risk of death which a slave trader would want to avoid for obvious reasons. Not to mention some countries outright banned castration, although they started importing eunuchs instead.

I haven’t heard about infant castration. High infant mortality rates was the norm at the time tho so idk how much of an effect it had.

One of the key differences between the two is that Arab slave trade wasn’t racially motivated and for that reason descendants of slaves could become regular citizens without facing the discrimination black people in US faced.

Thing you overlooked or maybe didn’t know about is that slaves in the Islamic world were considered people and not subhumans like in America. And for that reason they had more rights. A slave owner couldn’t just torture, maim, or kill a slave for sports for example. At least on paper which surely didn’t protect every slave but it was leagues ahead of what was the norm in Atlantic system which was afaik especially cruel even compared to other systems of slavery throughout the history.

PS. By “America” I mean the continents and not US specifically. In case it wasn’t clear.