There is indeed a huge difference in the slave stories before Columbus and the Portuegese but these stories are rarely told. This is specifically about the Barbary Pirates, initially part of the Ottoman Empire as you've suggested, but there's a balance that comes with writing pieces entertaining enough to be read all the way through and informative enough to be discussion worthy to those without an interest in history. It's a difficult balance that I call 'infotainment' (Dan Carlin-ism). There is definitely a lot more to read around the whole subject and plenty of history off the beaten track (much of which you've mentioned).

What I would say is that many people, particularly those in America seem to believe history began in or around the 1600s and that there is one type of slavery and one type of story to tell about said slavery. The question is firstly, why? And what are the psychological implications of such limited creativity. The idea of telling the story about the Barbary pirates seems like it would be offensive - but why? And what does that mean? Does the magnitude and severity of the Transatlantic trade render all other historical stories null and void? And if so, why? I don't want to get too bogged down in the history - and I know that can be frustrating for historians like your good self, but needs must when it comes to readability and opinion pieces. :o)