TTv2
There is a reason the alternate calibers are available. They are not as good. while they say at Gunsite "any gun will do if YOU will do" I prefer to swat flies with a flyswatter rather than a stick.
You could make that case about calibers like .32 ACP, until the last few years defense ammo was all lacking, but we've got evidence now that shows certain loads like Hornady Critical Defense and Fiocchi Xtrema are capable with a long enough barrel. You could also say that .380 and 9x18 not being as powerful as 9mm, yet costing more make them "not as good" but the goal for self defense isn't what works better, it's plainly what works.
There was a very detailed study on real world use of calibers done years ago that a lot of people have cited and I recently took the time to watch videos that did a good overview of the study and what surprised me was that the .380 was about equal to 9, 40, and .45 in terms of successfully stopping an attack. That really opened my eyes up to what .380 and 9x18 are capable of and if used in long enough barrels combined with a good defensive ammo, they'll do the job.
Calibers that are as or more powerful than 9mm, but are still "alternative" calibers, stuff like 7.62x25 and .38 Super... they're all just as capable as 9mm or .40 are, but they're limited in variety of guns, limited in ammo variety, and accessories. They're not useless, they will work, but you have to really question which one you'd rather have and which caliber is likely going to be available in the future.
For the record, I don't view 10mm as an "alternative" caliber, it's far more popular and practical than all the actual alternative calibers.