Look, somebody will always have a success story with your pet caliber, even a bb gin, blow gun or 22lr.
It can also be argued that 5.7, 380, 9mm and other small calibers are good SD calibers, multiple test results and actual shootings show calibers larger in size which normally expand and still penetrate 14" are the best for self defense. When plugged with clothing, I would still rather be making 45 holes vs 22 holes. 14" gets you through even with a light barrier. Hunters know exit wounds bleed out, so you have to get through. In addition, the spine is in a human's back, covered with bone.
So 40+ sized calibers which can be shot fast are best for sd.
If completely impractical, I like things which will penetrate and shoot fast for caliber like 357 mag or 38+P. These should keep the 14" penetration and be more likely to expand due to high velocity for caliber.
Last, if you need to hide it in a speedo, lesser calibers in fmj should at least penetrate to the spine and give an exit wound like 32 ACP or 380.
This is why I struggle with 9mm. Then bullets need to expand to stop, but they often penetrate less when they do. The gun is usually as big as a 40. The only good thing is 9 is easy to shoot fast and the ammo is much cheaper.
The 22 has cheap ammo and is ideal if attacked by prairie dogs or other rodents and snake. A good utility gun and the ammo is light. Hiking, I would be tempted to carry a 45 for sd and a 22 with lots of ammo for fun, snakes, survival, etc.