I mean, this far back in history - I find it hard to say Cleopatra as a figure that has anything to do with the modern Greek or Egyptian nations or cultural groups. I agree that when possible, we should use these roles (like any roles) to give opportunities to actors who don't usually get them - In that regard, the casting is problematic, as Iranians and Muslims in general do not usually get cast the lead roles.As much as Gadot is Greek. He looked the part of an ancient Iranian, as they were pretty "white."
The point is once you start trying to account for cultural migrations over the centuries you've already missed the point. Having Egyptian, Greek, or Iranian actors portraying important roles from their nations' histories is about more than getting a skin pigment "correct," it's about using these opportunities to make sure those underserved communities are represented in front of the camera.
But for Cleopatra - I don't think Greeks are very underrepresented compared to Israeli Ashkenazi Jews? or that there's even any power dynamics between the two groups that would make this decision problematic in that regard...