Where DO you get your information? While a 9mm isn't in the same class as a .45 ACP, it certainly has enough to do the job providing YOU do yours, especially if loaded with the proper home defense rounds!
AND, loading a 12 gauge with deer slugs for home defense is quite possibly the worst bit of advice I've ever read. Personally, I don't care if I have to replace a television, a computer or a piece of furniture. A shotgun's pattern, even from across the room (say 30 feet)with #6 shot is going to have about a one foot pattern. IF you do miss the intruder, it's not going to be lethal once it's gone through a couple sheets of drywall.
NOW, what's going to happen with that 1 oz. deer slug if you miss? It's going to penetrate both layers of drywall that make up an interior wall, barely slowing down, continue going and likely exit the house unless you live in a brick home. And what happens if there's someone sitting or sleeping in that room that the slug passes through? Would you really rather shoot the TV or a family member?
That's the reason why all the shotgun defense articles I've read all recommend using shotshells in a shotgun. The only time I've read about slugs for self-defense is to keep them in the buttstock mounted shell carrier for when you need to shoot farther out, as in the intruder has left the house and is making a getaway.
Formerly Steve @ G & S