How Much is Too Little

That's a good article. I personally use a 45acp exclusively for self defense, but I don't think it's the only solution. I cast my own bullets and I reload. The 45acp is such a low pressure round that I realize a very long lifespan on my brass. Also I'm able to cast bullets from wheelweights as opposed to having to use a custom alloy to take the pressure. This is not to say that I use my reloads for defensive use, but it does allow me to practice inexpensively with a simulated full power round.
One of the things I caution my students with is that if they are going to carry a caliber that requires a boutique defensive round to be effective, they need to stockpile enough of it to weather these ammo shortages. Otherwise, I would recommend the largest caliber that they can control.

The last lines in the article are:

"While there are infinitely more effective self-defense calibers available, a functioning pistol is better than nothing."

Circumstances sometimes dictate what one carries. As such one should become proficient with whatever firearm they choose to carry. While I would always prefer a .45 Government Model at times this is not practical or possible. A .22 would never be a first choice but it is certainly better than a pointed stick.........