It is all a question of balance and, as you said, faithfulness.
I will repeat myself by saying this, but oh well...
It needs to be a useful weapon. In fact, in real life (if anyone comes with the realism argument) you are in the same stance if you have an AR33 (M16) or a PP7 (PPK), i.e. at close range (thus obliterating any accuracy-related issues), if I shoot you with the pistol, I don't think the rifle will save you from anything. of course the damages dealt by each weapon must be different due to the nature of the projectiles shot by each other. But, and I say it again, this is GoldenEye and the PP7 is like a sniper rifle without the scope and twice the awesomeness. One advice: if you want realism, or as close as it can get of real life, when it comes to videogames and weapons used therein, go play America's Army.
'Nuff said.