That's crushing Nungali, but you haven't really answered anything, just pushed it away.
I believe it'll be hard to stick to Atlantis solely, as long as we don't establish what the Egyptians could and couldn't do.
Better do that than to mess around trying to make sense of some psychic's accounts.
But you've got a point. Someone, somehow built it. Just like anything else. Clearly they didn't have building cranes and diamond plate saws. It took people 200 years to build Notre Dame. Isn't it more likely that the scientists got their "20 years" wrong?