As a workers comp case manager, I’m fairly knowledgeable when it comes to work-related hazards and injuries-it would not account for an increase in serious injury like what is described here-that is more likely to be a result of stress caused by too many humans living in an area with not enough resources or space for that large a group. Many studies have been done on the subject-people do not do well in hives...
With bronze age tools?
These cities would not have been hives and living in a tribe would not have been the free and solitary existence you seem to imagine.
The people in the cities would have had more food, more resources, more safety and space then the people in the HG tribes. There was a reason people moved into cities and it was not because they couldn't move their couch.