It'd be a waste of resources to model those mountains if the player can't get any closer to them. Static backdrops are a smart choice for many a game, even if it's just a sky box. As for the game looking close to that, have Insomniac ever misled in that respect? The original RFoM images were true to the final game, were they not?
I wasn't trying to degrade anyone's work, just stating the impression I received from those screenshots is all. They look absolutely fantastic. Too good for me to believe initially.