Caliber doesn't matter. It's all about shot placement.
So your home and/or self defense weapon is a .22 or a 32 ACP or something?
The all about shot placement stuff slays me. While hitting the vitals etc. certainly is #1, it is NOT everything. Not at all. Hitting the CNS or center punching the heart lung area in the dark, under stress, on a moving aggressive target that may well be in the process of hurting you or a loved one, from a less than ideal position, perhaps while hurt yourself, and doing it all in probably just seconds sounds so easy.
There may well be a good reason why one of the more ideal home defense weapons is a 12 gauge with buckshot and not a Marlin .22 auto.
Most LE shoots, and most HD shoots have a hit probability of 20 to 25 percent. That is a hit anywhere. Practice and skill will increase the likelyhood of a hit somewhere on the target. An adequate round will increase the likelyhood of a hit making a difference. In that I find myself to be a desirable person to save, I will continue to stack the deck.