Suspended
I would suggest that the talk isn't so much about it being "non factual", as films have always twisted history, but more changing the facts so that people who we all acknowledge as "The Bad Guys" have had their history changed to make them into the "The Good Guys" and film then wants us to support "The Bad Guys who have now been changed into Good Guys". I would say that makes the difference between this and virtually every other "based on true events which have been twisted to make a film" movie where the bad guys remain the bad guys.
We had the fictional story of the Dora Milaje in Black Panther, who were based on Agojie, and no-one complained about them to this extent, because the story was fictional so most people seem to be OK with strong black women fighters which is why I'm very surprised that Maria Bello, the white middle aged female writer of this film who was the driving force behind getting it made, after seeing the positive response the Dora Milaje had already got, was willing to leave behind her liberal/progressive mind-set in a deliberate effort to tell the story of these slave traders by making them into "The Good Guys".
I do wonder if, although unlikely, the project hadn't been so heavily pushed as "Based on True Events" etc and had instead started with "A fictionalised account based around True Events." (kind of like the 300 movie did vs the 300 reality - I know the movie was based on the graphic novel) that the reception might have been better, but I really do struggle with the studio's understanding of making bad people into good people to sell your movie, how was that ever going to be a good idea?
I'm waiting for the Adolf Hitler story. That of a brave artist whose vision of a beautiful and united people was foiled by those pesky Jews and the foul Westerners who just couldn't stand to see a noble race making it on their own.