The Sphinx wasn't built with stone from a quarry, it was carved from the bedrock. It has since been restored a number of times, one of which added layers of limestone block which is easily distinguishable from the original shape.

How did the erosion happen? At what time period was that much water there?

Also, Schwaller de Lubicz was very loco and racist (very antisemitic and was close with a number of the earlier ideologues of the Thule movement)