I think you are overestimating the precision of ancient pyramid blocks. Most of them are quite crudely cut, with the gaps filled with rubble and mortar.

Speaking of the Great Pyramid, the bulk of it is crudely cut, but the outer casing and the lining of the interior chambers has gaps well below 1 mm in width. These stones are about 2.5m long, much longer than a typical human, and weigh several tons. Not only had they to be cut to sub-millimeter precision, they also had to be installed equally precisely. This takes serious engineering chops, especially when you don't even have steel.