The reason for advent of behemoths like Lomu was the allowing of wholesale substitutions. This meant that players no longer had to play the full 80 minutes and so endurance could be sacrificed for power. This in turn has likely contributed to the increase in serious injuries in the game, particularly concussions. Rugby has changed a hell of a lot since the advent of professionalism in 1995 and they probably need to row some of those changes back imo.