If you visit modern-day construction sites where they use large concrete forms to pour entire floors and walls at one time, you'll notice the construction of those forms is from steel to hold the weight of all that concrete, and also includes steel rebar within it to give it more stability. If you don't have steel yet, you have to build with smaller blocks, and the gaps between the blocks protect against cracking from expansion and contraction.Why not simply build a form that casts the concrete in one solid piece? See any large construction site for examples.
It also makes sense to me to use different materials for the foundation (lower layers) than for the upper layers, just due to the amount of weight each layer needs to hold. Bringing in whole blocks for the lower levels may have been stronger for a foundation layer, but once the pyramid got too tall to lift/hoist those large blocks in place, carting up the rubble (perhaps it was also a "thrifty" use of the chips and dust left after cutting the blocks at the base out of the quarry and fitting them on-site) and using it as a cement to form the blocks on the upper layers.
I don't think this necessarily changes history though, since it still would require an immense amount of labor to do the construction, it's just a difference on what the labor was doing and where the technology existed...chemistry/materials rather than apparatus for hoisting/transporting large blocks of limestone. But, the reason there were so many different versions of how the pyramids were built (i.e., slave laborers, paid laborers, was it just vast numbers of laborers doing a lot of heavy lifting, or did they have the technology to lift those large blocks with less laborers) is that it remains quite speculative.