In Raids and even Strikes, the enemies are bullet sponges and often shielded. Shotguns require you to get close. No Shotgun is going to kill a miniboss in one shot. With the slow reload and small mag capacity you also can't pump enough shots into him to finish him off before the rest of his swarming minions get you. For shotguns to be effective in PVE you need the 200% damage increase which is good but you also need a huge range buff increase to give you that time to manuever and reload. It doesn't matter how much damage your shotgun does if it requires being in melee range because by the time you reload for that second shot you are dead by some other spawn minion.