In all honesty I think that the weapons have been balanced extremely well. The pistol has not proven to be useless at all,
nor has it proven to be
better than mainstream weapons for me. I can go toe to toe with anyone who has any weapon (Excluding snipers and explosives, of course.) and feel like we've had a fair fight. The pistol is extremely good for
helping a teammate with a kill, or for stealing it outright. If I could have any wishes for the pistol, however, it would be that it would include just one more shot than it does. I always have to reload after I break someone's shields and that usually results in reloading and death
All-in-all, the pistol is good for medium-range secondary assaults. It's also decent for quick damage and headshots, especially if you have good aim and can hit the head of your target. However, the BR, DMR, and Carbine still beat the pistol--in my experience--for medium-range shots.
I'd like to dive into that AR claim you have too. I'm noticing that if I let anyone who has an Assault Rifle come too close to me, I can consider myself as dead anyway. They're just good for mowing down your opponent. If you're trying to run after someone who has an AR, and you're just using a pistol to try for a quick bash and clash, the AR still has a fair advantage as long as its wielder can shoot straight. If you take your time to watch someone through your pistol scope, and shoot them before they notice you, chances are you can pop down their shields, reload, and come back for a finishing headshot before they can even break your shields. Distancing and practice have a lot more to do with the way guns work in Halo 4 than I've seen in any other Halo game to-date.