Weapon redundancies existed already though, after Halo 2 anyway (and even it had some), though this does depend on how strictly weapons are classed. Halo 3 has the Spiker, AR, SMG and Plasma Rifle, all arguably filling identical role. The BR and Carbine share a role. The Beam Rifle and Sniper Rifle are nigh-identical. Reach does the same, though it did admirably try to differentiate some weapons (eg the Sniper vs Focus Rifle). EDIT Reach had issues with counterparts being worse for most part though. The Needle Rifle was arguably worse than the DMR as general purpose weapon, and the Plasma Repeater was pretty bad compared to the AR.
Granted, Halo 4 did add even more weapons, but what is few more on top of already large sandbox? Not much, and 343i also tried to add unique characteristics to the new weapons at least. Admittedly balancing wasn't quite there... but then it is not like Bungie ever got that nailed down either. It feels like neither even tried at times, to be honest.
Figure redundant weapons are less problematic than how and where they are used. A map should pick only some weapons of the sandbox, and another similar map could pick other weapons, leading it to play differently. Would be interesting to have maps where the standard utility weapon isn't the BR but the Carbine or Needle Rifle, and instead of Shotguns there'd be Boltshots, or any other such unusual combos. "Mix things up a little".
And occasionally some weapons should stay in the campaign (looking at the Fuel Rod Cannon especially here, though the Promethean power weapons are as big offenders) and custom games.
