Let me guess: Netflix?

From the outside (I've never worked at any of FAANG, I don't even work in the US) it seems to me that they are the most likely of those companies to actually hire seniors as seniors, simply because they appear to have made hiring preferably seniors (in terms of experience, not in terms of age) a strategy, while the others all seem to have made hiring huge numbers of inexperienced juniors their strategy.

It's Facebook. I've met plenty of people from other companies on that list without a university degree. Although, engineering levels are not something that people usually talk about outside of their close social circles.