That's fair enough--in any slave society, there's a decent chance that any sufficiently large body of unskilled labor contains slavery simply because some non-negligible fraction of the labor force is slave.
That said, I interpret a statement like "the pyramids were built with slaves" to refer to an idea that the vast majority of the workforce were slaves, as for example was the case for agricultural workers in the antebellum US south (although apparently it was roughly 6 free workers : 7 slave workers specifically in agriculture in the region, a somewhat lower ratio than I would have expected--I guess I'm undercounting the existence of non-slave agricultural lands.)
That said, I interpret a statement like "the pyramids were built with slaves" to refer to an idea that the vast majority of the workforce were slaves, as for example was the case for agricultural workers in the antebellum US south (although apparently it was roughly 6 free workers : 7 slave workers specifically in agriculture in the region, a somewhat lower ratio than I would have expected--I guess I'm undercounting the existence of non-slave agricultural lands.)