There are millions of concepts attributed to one period, in which there's proof (documented) that were utilized long before. History is all about the credit.That doesn't make a lot of sense...theories today say that the pyramids would have been built within the lifetime or prior generation of these scholars and mystics operating these schools. That would be like you or I not being able to identify who built the original Sears Tower or Trade Center buildings.
These scholars though not native to the land, would have no reason to suppress or hide the history of a nation they admittingly acquired a great deal of their understanding of the world from.
The average block that makes up the pyramid of Giza weighs 2.5 tons...what kind of trees and how many do you think it would take to move as well as lift those types of carved blocks?
I was at our science museum last year for adult night. They had a standard pyramid block adjusted weighed for the equivalent, and they let you play with it, showing how it was pulled, with just some rope and a board. As for the trees, you're missing the concept of pulley/lever system. It reduces the weight, so that it's easier to lift/pull. As long as whatever you're using is solid enough, you can lift/pull anything using its own weight as leverage. That basic concept is still used. But that's probably why he said "enough people."