no, the exceptional aspect of the American slave trade is not first and foremost the “industrial scale” but rather the utility of this topic for people who are out to continually shake down the non-black people living in certain West Hemisphere nations for money to give to the descendants of the slaves. Or at least try to start such a shake down, case in point being Brazil where the project has not yet really gotten off the ground so far.
As far as the industrial scale agricultural slavery goes, how about 9th century Iraq? See here Zanj Rebellion - Wikipedia . Judging by the numbers involved those black African slaves employed in, yes, industrial scale agriculture, constituted a huge percentage of the regional population, sort of like some areas of American Deep South or Roman Sicily in other epochs. So yeah, pretty industrial - but where is the money here? Who is going to give grants to Jessy Jackson in recognition of this Iraqi slavery of umpteen generations ago? Especially since those slaves apparently were never allowed to procreate sufficiently to survive as a distinct ethnic group, let alone as surprisingly relatively unmixed as the American blacks.
When it comes to figuring out which atrocities are exceptional and which are not, it pays to go for where the money is.