Yes, we should exclude Qin china (at least until very late in the game development cycle) because Han China is in. Mamluke is more detable (Mesopotamia vs Egypt, Arab dynasty vs slave-warrior of diverse origins Dynasty), but we certainly should not have the other Mesopotamia-centric caliphates.
At the end of the day, we only have so many civilizations, and it's remarkable how often people forget that. Qin may be nice to have on paper, but at whose expense should they come? Korea? Vietnam? A whole variety of other Asian people who are far more diverse from Han/Qin and from each other than Han and Qin are? That's the real question, and the presence of Han make Qin less essential.
LIkewise for extra eras. Dividing sixty civ between four era instead of 3 means five fewer civilizations in each era, alls so already-represented areas can have yet more representation,,. Sorry not sorry, this is a terrible idea.