In my research on population densities, the closest I could get was for the Medieval period and was based on the maximum output of arable land. Assuming the Medieval farmers didn't make too many improvements to crop yield over their classical forebearers, the population density of Egypt would have been between 12 and 48 per square kilometer. Egypt is mostly desert with a big river running through it, so I'm inclined to go with a lower figure of maybe 20 per square kilometer. Two million Israelites would've required 100,000 square kilometers just for their own support. If the habitable region of the Nile extends 50 kilometers out to either side of the river, then 1,000 kilometers would have to be devoted to just supporting these folks. I'm not certain how much of the Nile the Eqyptians of this time claimed as their own, but even if it was 2,000 kilometers the Israelites made up fully half the population. Such a mass migration would have economic repurcussions far outside Egypt, as trade would be disrupted (half Egypt's export makers would be gone, along with half the Egyptian market for importers).
It's pretty much for these simple reasons I've rejected such claims as David commanding 600 mercenaries during his formative years in the Levant. I can see 60 guys being possible, considering the productiveness of the land there, but 600 would be a major chunk of the population.
Interesting post.
Just a thought, though. When Heinrich Schliemann discovered Troy (the Troy of the Iliad) there was virtually no one who believed that Troy existed ever. Schliemann believed it. He was basically alone. He believed that the Iliad had mostly fact.
Nowadays, most archaeologists accept the fact that, he did, in fact uncover Troy somewhere in Turkey. It's a pretty amazing accomplishment if you think about it. Also interestingly, he had to dig down through eight cities on top of each other before he found the "real Troy". And the scientific community of his day didn't even know a city had ever been there.
So...the point being. I don't think we know as much about the world as we think we do. I'm not commenting on your particular post, incidentally. I'm just interjecting a cautionary idea into our thinking about antiquity.
At the end of the day....it turned out that the mythological Iliad was more accurate than the science of Schliemann's day. It may turn out that Exodus, though dismissed by most as mythology or pure fabrication, is factual.