You don't get it do you...
RL is players are spread across a field not along. Compare that to soccer, hockey, basketball etc. You can know a position by the players place on the field (90% of the time).
In RL a winger can come in on the first tackle and take a scoot, this does not mean he is a hooker to the untrained eye who might think the guy who picks the ball up is the dummy half. You could almost use that kind of example with any position in RL depending on the time of the game, the tackle count and the teams style of play.
I shouldn't need to explain soccer or hockey (basically the same kind of layout along the field).
Basketball has a PG who has the ball at the start of a possession, G's along the perimeter, and PF/C in the paint. Simple to grasp with 5 players on a court/team.
The NFL can make it work because the game is easy to grasp as the roles of individuals are simple (but as a team are complicated) plus you have the benefit of stoppage rather than rolling play with set positions each play.
AFL is the 1 exception when it comes to positions along the field as the game is a sh*tfight for the ball anyway it is hard to follow with or without numbers.
RL you can have a 2nd rower in the centres, a Fullback or Lock playing 1st receiver, 2nd rowers up front, 6 and 7 switching between scrums/receiving etc.