Any player is capable of 80mins but not at total intensity, Levi can play 80 but his zip will diminish towards end of each half like most players in most positions. It’s a matter of is his last 10-15 of each half better than replacement. I think we put to much emphasis on playing the 80 or not, at hooker you need someone to cover him due to injury as well as fatigue. You can cover other positions with fwd playing centre, wing playing f/b but 9 is a specialist position. If a player goes out assuming he is playing for 80mins then he paces himself, goes flat out when opportunity presents itself, gulps in the big ones when opportunity presents itself and looks to others to cover when need arises, it is a team game, all 17.