You do know that the difference between a level 24 and a 28 has nothing to do with how much damage their weapons do, right? A level 20/ legendary/ exotic shotgun with the damage maxed out and a high impact stat will kill a level 30 point blank. That's what shotguns are SUPPOSED to do. They're close range weapons. Even if it were affected, there isn't much disparity between the armor stats between a 24 and a 28. Arc blade has risks. One of those risks is getting close enough to the enemy to be in shotgun range. If that doesn't suit you, go back to gun slinger and stay out of range.