Ok so from what I understand and I can only check my niche as thats all I care about. There are two major winners...
1. Big brand
2. Mid Brand (in same bracket as me)
Have seen big gains and in some cases competitor 2 has knocked me from the top spot and I now rank pos.2 rather than pos.1..
From what I can tell Big brand has had a make over and restructured content and brand 2 has reformatted all of it's content. Looking at other sites and competitors as well it seems those who have had gains seem to have tweaked the UI or have been reformatting the content.
Our site due to the mass in demand this year has been rather static we could publish a page and rank almost instantly - we tried this with a few products this year and it worked well now the content is all unique and isn't spun, but since the update we have dropped.
From what I can gather we have been effected on two fronts:
1. Pages with the old content layout have dropped a fair bit
2. New pages with a revised product layout (in terms of optimising the page for snippets) have done well BUT no where near the positions they used to be.
My thoughts from my own niche at the moment is sites that have reformatted and improved content have done well, sites that may have remained stagnant have not. Don't get me wrong our blog is active and so is our social media but the main site pages have not improved at all for the very reason they may not have required changes.
It's just a guess but this seems to be a "fresh & care" update in my opinion, and it's only limited to the 50-80 sites I watch in our niche (Home & Garden)
I think those that seem to have come out with new content ideas and improved the page have done well and those who have stuck with just posting anything or nothing at all have dropped. Which I guess is "fair"
What I will say is a competitor who has a private PBN (that I am aware of) with spun and rehashed content or had it outsourced have dropped hard - but this could also be down the their PBN or anything else being discovered I guess..
A few coffee sites I visit with mass authors 50+ seem to have dropped as well but I don't know if that's related to mass content or they are spinning content or something totally different I've not had a deep dive into it all outside of our niche as I have said to confirm this or not.
Again I've only taken a small sample pool of data I have had I'm no SEO Guru by any shot of the imagination, but to me this update seems to be based around content / information.