I don’t know if it’s “old news” but thanks for your post. The double-blind technique (also called “horcruxing”) does in fact add another layer of security.
I tried using it on a couple of sites, but quickly decided it was more trouble than it was worth. You have to type in extra characters at each login. And Bitwarden notices that it’s a different password so it pops up a little nagware window that you have to click on to dismiss. All that for the extremely unlikely possibility that someone might “acquire” my master password.
It’s not for me. The whole reason I use Bitwarden is because I’m lazy. Double-blind passwords make me work too hard.