I believe from my perspective I would then ask you what is it in your opinion that makes an RPG different from every other game. Is it the classical party rolls around to crush villainy and save the world. Or is it merely a game that has a story behind it that one goes to accomplish.
If you go back awhile FPS has always had a story but shooters are always shooters as they have been classified as simulators. A simulator is not an rpg base. Thus eliminating halo etc from what I would call RPG. The other class of game that has always had a story but has never been classified as RPG would be RTS or strategy (different types both strategic) The remaining types where all rpg's or arcade.
FPS and TPS were originally considered simulators then they became popular in my mind they are still simulators.

