Archeologists would be able to find evidence of these water piping from springs underneath the pyramid.
I agree, they say that they should have found evidence of ramps... well they should have found evidence of this water structure if it was used.
The video says that they toke the water from springs under the pyramid. If the spring has enough pressure to make the water climb to 150 m, then just opening a vertical hole you must get a 150 m water jet. (Really, the water in the jet moves faster, so it has more internal frictions with the spring wall.) In Yellowstone, Old Faithfull has 50 m water jets, but it’s a geyser, not a cold spring with a lot of water.
They had thousands of slaves.
The pyramids were actually not built by slaves. There's quite a bit of evidence that would suggest this.
Were they slaves? I've often seen reference that they were citizens working on the pyramid as payment of taxes in the form of manual labour, add to that your boss and the building were being built for, who to them was, a God.
I'd say whatever the most simple explanation is the answer I could see either rubble or ramps.
They were slaves. Calling them something else doesn't make them less exploited.