The only way this would really matter to any question of honesty, which you have challenged by calling certain types of settings disingenuous, would be if state sponsored were a part of every culture, throughout history, always, and even then only when discussing direct analogues of a real culture, and even then it wouldn't make not featuring that in the fictional world at all, in any way, less honest or genuine. It's a fictional world, no one calls grimdark worlds disingenuous, but make a world that is a bit more aspirational/optimistic, and hooooboy it's "theme parks" and "disingenuous".
Slavery is not central or necessary to Islam, to Southwest Asia and Northern Africa, nor to stories about heroes in a mythical desert realm with a strongly dominant mainstream religion that runs across species and cultures, creating a shared language and common idioms and practices even in otherwise very very different groups.
Not including it is no more disingenuous than not doing a deep dive on medieval travel and making the PCs abide by the norms of medieval travel while adventuring, or allowing female characters to be knights without ostracization.