MrFalconfly said:
Exactly.
It's a fantasy. A thought experiment. A "what if".
"What if Egyptians were white?" That sounds like a fantasy that has already been done to death.
Generally if you're going to use a setting, your changes should be somewhat deliberate. "What if in ancient Egypt the gods walked among the mortals?" is a cool premise and you could definitely do some interesting stuff with that, bringing mythology to life. Or maybe you want to have something deviate from historical accuracy because it allows for a more compelling story. That's also fine, you're making the movie better.
I'm not sure "It's fantasy, they don't have to be at all representative of reality" really works in an argument. Sure it's fantasy, but people would probably be complaining if at the end of the movie someone decided to walk on air and it was never given any explanation or setup. A fantasy setting doesn't give you license to ignore reality carte blanche, it just gives you the freedom to when doing so makes the setting more interesting.
Hell, I don't hear the same argument coming up in Lord of the Rings when people comment about how white everyone is in it. The response is always "It's a setting based on medieval England, it'd be weird if there were black people". I suppose it just isn't weird when we do it with Egypt because we're used to seeing the rest of the world depicted as white