wow... well that is a different philosophy. I suppose it could work if you built up to it but forwards and outside backs that run the field a lot would be at a pretty high risk of injury getting there and the team would be highly vulnerably as those tired defenders try to run down fresh forwards from the other team.
They've done it for a while. when their are injuries, it gets rough and the criticism flows. When the injuries are minimal, playing time is aplenty and parents are happy. Fitness lessens injuries but they do happen. They spend plenty of time on the field for sure. They also dedicate recovery time. It's a delicate balance and not for everyone.