Interesting thread.
I think .380 can be a perfectly adequate caliber for self defense, HOWEVER, alot of the small pocket guns in .380 have so so reliability and short barrels that make .380 even more anemic. In my mind its almost like they are two different calibers.
With the hornaday XTP bullet in a Walther PPK or a shield EZ or the .380 walther CCP with a longer barrel (and 100fps more velocity), your right on the edge of still having expansion with acceptable penetration. It wouldn't be great as a service pistol, but I think it would be okay as a CCW. especially in say a shield EZ that is a gun that isnt too difficult to shoot with. When you get into the really short barrel LCP Kel Tec type stuff, you lose enough velocity that either expanding ammo wont expand or will underpenetrate and ball seems to be the only choice. But given how those smaller guns are hard to shoot and especially with a more anemic round how important shot placement is without a bunch of training and regular practice I would find it an unattractive choice.
Honestly though, having listened to the snubbies modcast and having carried a pocket .380, I would rather have a snub .38. Small .380s are likely to be carried on the ankle/pocket/bug/deep cover and get a bunch of crap in what is already a soso reliability gun. In addition, while still having crap velocity, you can haver a much heavier bullet with more momentum for very good penetration or some decent terminal ballistics with +P loadings.
Something else to consider with .380 is if you carry ball, most ball ammo isnt that great quality, especially given the ammo shortage we are in which has thrown ammo quality even lower and you have an even greater issue with malfunctions. Versus with a snubbie, unless your gun gets blown up or you somehow have a squib with that short barrel you can just pull the trigger again.
Heck as a science experiment for the DIY gunprinting guys, with (very carefully measured charges, 0,1 grain steps up of powder and a chronograph), I reloaded some ammo with the cheapest wadcutter factory seconds, a lee loader kit, and nail gun blank powder and never had a single bad round or malfunction in my J frame.