But the logistics of keeping that many slaves permanently don't really add up. If you have them there 24/7 then you're responsible for feeding, housing, clothing them, and having a large slave-master apparatus costing you a lot more. Having a few slaves/indentured servants per household is reasonably efficient, or plantation slaves in the Old South, but only because the advanced weaponry of the firearm meant a small number of guards were needed. but there's literally nowhere where for example a "slave factory" is overall more efficient than merely paying people a wage then sending them home at the end of the day. There's a reason that the places with "wage slavery" are economically beating the places with actual slavery.
Also, we don't have any evidence of any archeology that supports the slave-hypothesis, so it's kinda disingenious to assume that the slave-hypothesis is the working hypothesis, until 100% proven otherwise. You should go on "preponderance of evidence" if there are two competing hypothesis, not pick one as the automatic default, without providing a compelling reason why it should be so. "because people used to believe that" is not a compelling reason to continue to believe something, when the available evidence says the opposite of the common-belief.
for example if there were lots of slaves worked to death (which you'd basically have to do, to make it at all economical vs simply paying farmers to come work on the pyramids during the off-season), there should be huge mass-graves full of dead slaves near the pyramids, but these mass graves do not exist. to the best of our knowledge. They would have had to put the dead slaves somewhere. We only have examples of people freely buried along with personal possessions and the typical Egyptian gifts for the afterlife, which would imply they weren't slaves, unless they treated the slaves especially well. Until we find the bodies of the proposed slaves, the working hypothesis should be that the existing, actually found, graves are typical. About 10,000 people at a time worked on the big pyramids over 30 years. Assuming a slave would last 5 years on such a project, we're talking 60000 corpses per pyramid that should be buried around there.