Never thought of that system that way. You do have a point though, it does give you an advantage, but, at least in Deus Ex, it is hardly jarring, because you also have 'player vision' aka you can see enemeies through walls, but also the fact that many interactions make you switch to third person, like climbing ladders, speaking with NPCs and enemy melee takedowns. Then again, I can see that it does not have that much of a seamless integration in the Rainbow games, giving an unfair tactical advantage in the game.