The Mayans are the only civ with enslavement in the normal game (IIRC). I think this fits. You can't have every civ with the enslavement option, that would make a glut of slaves.
I pesonally think it is fine as it is. The Mayans, while they are strong, aren't THAT powerful. Industrious has been toned down, Agriculturual isn't that useful until you are out of Despotism or if you start near rivers, flood plains, or deserts. Their unit still has 2 attack, so it doesn't win all the time, and they have an iffy time for their Golden Age.