Killed truckloads of Deer with 12 and 20 gauge slugs when I was in my teens. Back then only a few shotguns were available with rifled barrels. It was smoothbore barrels and front bead sights for most of the guys I hunted with.
Fifty yards was as far as most of us were able to hit a gallon milk jug with that setup. Then came the Lightfield slugs and rifled barrels. Decent groups at 100 yards became common, but most shots were in thick woods at 30 yards or less.
Most Deer that I've seen take a shotgun slug in the boiler room didn't make it 20 yards. Seen hundreds of them shot with shotgun slugs when we could still do drives with large groups of hunters in eastern Ohio, but this was in the 1970's and 80's. Most of those large properties have been broken up now, so hunting on a few acres from a tree stand is the norm.
Shotgun slugs can be extremely effective at short ranges, but lose energy rapidly. Even the best rifled slug setup is a 100 yard max setup in my opinion. Beyond 100 yards, the straight wall cartridges make more sense.