Yeah you make some good points. "useless" probably isn't a good choice of words.
Though I'd say a Kahr PM9 is pretty damn small and there's really no reason a woman couldn't just as easily carry that in her purse than a .380 and shoot the mugger in the face with 9mm +P instead.
A PM9 has a list price of like $780. A Glock will probably have a list price down in the $450 range.
$330 is a lot of money to a lot of people.
I'd be willing to bet that if you gave those prices out to the vast majority of people looking to carry - they'd say "WTF" to the Kahr price and buy the Glock instead.