Sacred Haven of Debauchery

No, there isn't much of a difference if you're shooting within the effective range. The spread is very slight, or it spreads in a line if you attach a barrel extension. But the issue isn't that, it's that first, the damage is twice as high as that of any pistol, but the range is the same, so it's IMPOSSIBLE to compete with rifle users. And if you do manage to get close, the shotgun consumes too many action points. In 95% of cases, you won't be able to fire more than once. And even if you fire the entire shot into the head, it's not guaranteed to kill the opponent instantly; in their turn, they can take down a fighter with a couple of shots or a burst from a standard automatic weapon. And on top of that, the weapon itself and the ammunition weigh a lot. Overall, it's all downsides.