25 year old site, medium-large, well established, first mover in our niche back in mid 90s, 20,000+ referring domains backlinking to us. Not a major brand.
The second the core update started running on the 13th we started dropping like a rock. Down 20% sitewide now, and continuing to drop. We were clearly hit by some invisible sitewide penalty, as EVERY SERP listing dropped for us by at least a spot, in many case many spots. We do not use any black hat SEO, keyword manipulation, unhelpful content, etc. We trimmed out our thin pages to improve quality indexing significantly over a year ago, and updated a good chunk of our content.
For one of our main terms we are #2 in bing, #65 now in Google. This is the case for a score other major terms. Across all other search engines we are listed accurately -- top 10 for everything obvious. Google's simply broken and can't rank us properly. I think it has to do with the fact that we are 25 years old, and their algorithms just can't cope with the masses of noisy data that our site has built up over 25 years. We have a ton of 301s, thousands upon thousands of spam backlinks from malicious / malware / crap / spam websites, and likely GBs of click and bounce and other data going back over 2 decades. Whatever the case, Google is broken and can no longer rank us correctly. A few of us ancient site owners have noticed this trend over the past few core updates, but this core update broke the camel's back.
We are not alone here either - it appears a bunch of other 20 year old site owners I have spoken to have also seen this issue, and also got hit hard in this update. Perhaps because Google's ML isn't dealing with legacy data correctly they are unintendedly burying older established businesses like us deeper and deeper, while new sites with clean data profiles are flying up above us all.
Something I am seeing over our entire vertical is major generic brands ranking above us, even though we clearly have better content in the niche (it's not close, both in quantity and quality). So, take TODAY.COM for example. The TV show. Large brand. Anyway, they have a giant spammy page that hits all the keywords for our niche. And even though their show has NOTHING to do with our niche, they are outranking us and other big niche players. Same goes with BUZZFEED. Buzzfeed is now ranking in our niche by creating a single targeted page per topic, and because the are large they dominate that term. Being a household name now DWARFS by ORDERS OF MAGNITUDE all other signals. Don't even worry about site speed or quality content, or anything else. It's ALL about whether or not you are a nationally known brand or not. It's a joke.
ALSO: the section of our site that dropped the most (30%+) is a section where users typically will get an answer to their question instantly. The dwell time on those pages is typically very low, because we answer them directly, accurately, and succinctly. I suspect the new Helpful Content or Core updates are using CTR and dwell time a ton more than in the past, because our low engagement time pages are getting hammered. The pages on competing websites that are outranking them now are pages where the answer they seek is buried deep in a massive amount of text.... requiring people to sift through huge rambling pages to find their answer. It gives a greater dwell time, doesn't it... so, some really upside-down things added in this new update. But if my hunch is correct, CTR / dwell / bounce data appear to be having some crazy unintended consequences.