Exact same as your point. Openside (7 in most countries but 6 in SA, Argentina and France) is a fetcher and a link man. Blindside is a ball carrier, tackler and auxiliary lineout option. Left wing is an out and out speedster and try scorer. Right wing gets more involved in general play. Four different positions. If you're pulling somebody up on picking a 6 at 7, why can't you be pulled up on picking a 14 at 11? It's a completely pointless exercise.
Ireland play 3 hybrids in the backrow. Both O'Brien and Wallace mix and match the roles of 6 and 7 while Heaslip mixes the job of an 8 with the role of an openside. Saying somebody can't pick O'Brien at 7 in his
hypothetical Lions team is ludicrous. Who cares if he didn't wear 7 on his back during the championship? If that was the criteria for selection the Lions, Neil Jenkins should have been told to GTFO of the 15 jersey on the 1997 tour.