This sounds like I'm rejecting stonerowing in favour of dragging, but I'm not. It's simply that, having observed the mechanical realities of both methods at your two demonstrations I can't say there are grounds for favouring one to the exclusion of the other. If you have enough people, dragging is simpler, quicker and yes, less tiring - and probably doesn't even need rollers in many contexts. But if you have few people or difficult terrain then stonerowing, if they thought of it, would be viable.

My guess is that they would have thought of it and used it sometimes, both in it's own right and as part of a hybrid "dragging and levering" method to get over periodic difficult sections. To me, it seems rather likely that people who were dragging a big stone along would have others walking alongside with levers and the advantage of those would become obvious.