Never made sense to use a shotgun in pve because u really don't want to get that close to the enemies. A lot use snipers because u can clear out an area before ur even within range for enemies to know ur there and fusions are excellent for crowd control and do way more damage than shotguns with more range at the cost of their charge time. Shotguns never really could be used as a panic button either because they didn't do enough damage to take out anything bigger than an acolyte or thrall that managed to sneak up on you with one shot. After the damage increase from the weapon balancing update they may see more use for this purpose though