I think no history-based game like these should avoid historic reality. Slavery was very real back then and removing it from the game because it is not 'ok' with current ideology is wrong.
If anything, games like these are educational. I remember playing SHOGUN TOTAL WAR and got so immersed into it I read a lot into Japanese medieval history. I could probably pass a Japanese high school's history test.
Without that game... i'd still think samurai fought ninjas on rooftops and shot plasma balls out of their butts. (j/k).