Said it before and I'll say it again. This update is (these updates are) very obviously multi-faceted. It's not just one thing.
I've got way too many sites and way too many keywords I'm tracking to be fooled into thinking it's a single thing. It's too many ads. It's keyword density. It's anchor text diversity. It's affiliate sites. It's poor content. It's PBNs. It's ... on and on. No offense, but screw anyone who strongly claims they have the one single answer. The one cure.
I've got several sites that tanked. And a few of them have *NONE* of the above issues. NONE. I've got a couple sites that have good content, no ads, not affiliate sites, and have been ranking near top of page 1 of search results for years, and they tanked. I have a few similar sites that were totally unaffected.
The update was (the updates were) about more than one thing. I don't know what those things were. What combination of factors are involved. I have no problem with people tossing around their guesses, but that's all they are - guesses. Everyone want's the magic single answer (I know I do), but I don't think there is one. So it goes.