Um, feivel, yes it’s her speculation, and I’m equally entitled to make the point I made. I even get where she’s coming from, even if I don’t understand it.
The dividing lines you mention are a very different type, and give us clarity when deciding psak halacha. The only possible connection I can see is in levels and yeridas hadoros, but there is no way to know if that applies here.
No, I have no idea why R Kanievsky decided what he decided. It is a fact, however (and with no disrespect intended) that many do not hold as he holds. (I have several close relatives named Shira, for instance, including one whose name was basically picked out by the rebbe of her family’s chassidus.)
Some names also seem more modern but were in fact used long before the current era; I was very surprised to find out that my chassidishe great-great-great-grandfather named his daughter Tehilla back in Poland.