I really like Unknown Armies - I played a short campaign with some friends a long time ago, and had a great time playing “Jailbreak” with a group that hadn’t played anything but D&D and Legend of the Five Rings - but I am going on record as saying that it derives from a world that doesn’t exist. The concept of something being underground just doesn’t exist anymore - even the most obscure bit of information is available in two seconds with a Google search, or, if you’re really unlucky, a visit to archive.org’s Wayback Machine. Information just travels too fast and replicates itself too quickly for something like the occult underground to stay underground and be even vaguely plausible. Set it before, say…2002, and you’ll do okay, but we went through the equivalent of the Industrial Revolution with the invention of the Internet, and you can’t put toothpaste back in the tube. Although there’s probably a school of magic that’d let you do it.
The same thing holds true to some degree with Call of Cthulhu - Delta Green has some rationales for why the Mythos hasn’t become common knowledge, and I guess it’s plausible enough to explain why you can’t immediately access a copy of the Necronomicon on the Internet with two clicks. Delta Green is certainly popular enough as a game to justify its own concept - the government suppressing Mythos activity at any cost - but it would be interesting to sit down and see what would happen if you wrote a setting where knowledge of the Mythos had grown to the point where it actively affected society and civilization. Everybody knows that the human race in its current form is doomed, and they’re all scrambling either for an escape hatch or an accommodation with the Mythos; the people who aren’t doing either are resigned to their fate. I started writing up a setting based on the human race essentially going into quiet insanity all at the same time, with the PCs being the only ones who were able to maintain their sanity - by avoiding contact with human social structures - but I was writing it wrong, and it didn't go anywhere. I may pick it up back up again.
I think, in fact, that there was a section in a Delta Green book which essentially stated that the human race would eventually become a Mythos race of its own, like the byakhee or the Deep Ones. God only knows where, though - I think that it was before the reboot into a new game, maybe in the chapbooks. I think that there was also a section where they specifically say that people become Mythos sorcerers because they know that the human race is doomed, but again, I don’t remember where they said that.