My theory:

1) the temple under the pyramids were built before the pyramids, possibly, but not thousands of year. That goes against everything we know about the area.

2) as a person has has dug at those pyramids in South America, I want to say that there is little controversy about them. My mentor, a leading Incan and Quechuan archaeologist, has disproved many of the "alien" theories surrounding the pyramids of Central and South America.

3) of course there is a retaining wall around the Sphinx! The Nile floods like clockwork, and before the Nile straightened itself out, the meandering brought it right next to the Sphinx. You are right, however, about most of it being jungle, because a lot of it still is. And the flood you mentioned did happen, but never close to the time of even the earliest Egpytian Dynasties.