Well, I would guess that the reason for the bring-in rule is that each player has only a single card so that suits could be used to determine the opener. Once you have a mulitple-card hand then suits become trivial and you need some way to determine who starts the betting. I guess the "first" of equal hands is as good a way to do it as any, which would, indeed, put the players in the early seats relative to the dealer at an unmeasurably miniscule disadvantage in the game.