Yeah, but balance. The range on the shotgun in the original Halo was pretty absurd. Though shotguns do have a pretty short effective range compared to most other firearms due to the lack of rifling and the nature of buckshot. A shotgun with a rifled barrel and loaded with slugs would be just as effective as most rifles though.

Yeah I understand it's done for balance, just the fact I've used real shotguns before sometimes irritates me cause you know I'll be like "really that didn't kill him? I guess I have to be in melee range, where I might as well you know, melee"