The range was impacted because of 1) the wild netcode, and 2) the bullet travel/spread on the Battle Rifle. Combine both and it is not a fun experience. That's why people were thrilled with hitscan was announced in returning.
Difference between that and the other two Halo MP games, Halo 2's BR was both hitscan and 2x, but had its aim assist drop while the enemy were further away. Balance out nicely. The DMR's issue is the 3x zoom, because having hitscan is fantastic. There wouldn't be near as much cross mapping if the zoom weren't so accurate. And Halo 4's primary rifle, whatever it may end up being, definitely needs to be 2x and hitscan.
Also, nobody used SMG, Plasma Rifle, and Spiker because most of them were useless and they didn't start you with a dual wield weapon, thus no reason to pick any of these up. The Magnum was a piece of shit, bar none. Too many useless weapons in that game. The only useless weapons in others would be Halo 2's Needler and Reach's Plasma Repeater.