Bungie will balance the game out. They are masters at it. I bet the next patch will sort out all the issues you are so worried about. In the mean time, get better at shooting your gun. Based on your k/d in most games, you need to. I use the shotgun a few times a match. Very situational though. Mostly when I know another player is around a corner with a fusion rifle or shotgun. Other than that, the vast majority of my kills are from auto rifle and machine gun.