It just needs a small damage buff (10-15% I'd say) and a price reduction (on par with m14, scar, etc), but it's otherwise pretty much fine.
As with the other half of the classes in the game, support is simply overshadowed by sharpshooters with their asinine weaponry. By itself it's actually a pretty good class with good balance. Ammo is sometimes an issue but not if you're smart about taking your shots - you can't use shotguns the same way you use pistols and rifles. Shooting bloats with their heads cut off or lone crawlers will obviously deplete your ammo quickly for no reason. If you line up your targets and use the penetration to your advantage, shotguns are quite fine overall.