Almost all of the women (and some boys) captured as slaves were used as sex slaves and that probably whitened up the population in the north African Muslim nations. Most of the men were put into the galleys (rowing large boats for the Ottoman Empire) -- completely isolated from the women and not propagating the slave species like slaves did in the U.S.
According to Dr Sowell, at the time of the founding of this country there were more Whites enslaved in Africa than Africans enslaved in the US.
To adjust the “balance” a bit - the US was a minor market for black slaves. The vast majority went to the Caribbean and South America, notably Brazil. So a comparison of the various Muslim vs European slave trades have to be on a total basis.
As for the Berbers being white, one has to consider that their ancient ancestors the Numidians and etc. weren’t black either.
That theory is all wet. The inhabitants of North Africa historically have always been white. The people the Romans fought for mastery of the African Province were white, as were the Romans who colonized N Africa and the German tribes who followed. Vandals and others.