"We Eschew That"
Then you eschew the massive audience of lazy gym goers, bodybuilders, referrals from the latest Joe Rogan podcast, Tim Ferriss ..basically the entire casual health crowd that want's to pretend they do hardcore research but is jumping away from you due to the text heavy layout.
I read code,I like minimalism, I am not being personal here, your designing outside of a greater potential audience and leaning towards an academic/journal design. Any UX expert that has not pointed that out, is just a job title, Go back to them and demand an example or case study where their recommendations did anything .. the industry is wrought with fools
In years past, If you were to be searching anywhere in the nation for audits relating to whether your website was legally compliant under ADA guidelines (accessible) you would run into my team quickly. Stepped away from that angle, it's boring, but still necessary, You pointed out your body font color and it's relationship to the background, now examine all the other options - particularly link colors and your choices for fine print,citations and small text. There are plenty of easy scan tools that will show you deficiencies in contrast choices including your Chrome browser.
Neither of those comments relate to your loss in rankings though -- but are deficits in your previous partners decisions and whoever made final approvals and whatever "experts" you trusted. Fairly basic stuff there. Im on your side,impressive content, I would be a reader, I am just offering some fairly simple fixes.
"moved to cloudflare"
I use cloudflare. I use cloudflare on dozens of sites, I have never personally seen a correlation of a negative impact, or really see the bad neighborhood impact as being as significant as your drop was - but there are a lot of case studies and forum posts from people who swear by a cloudflare correlation to significant drops in positioning. It's worth testing what removing it will do.
I didnt call your titles "clickbaity" - im just referencing past comments and pointing out there is nothing wrong with them, but they should be page titles and OG titles, not meta titles.
If you dont know what I mean on document structure and on page optimization options - then I really have no idea what manner of SEO opinions you could have received, "we" all have different strategies and positions, but this certainly should have benn discussed with you.. as I kind of referenced, the printed "white hat" dont over-optimize crap is only good for selling enterpise seo consultations .. your superfoods article has 4 images named superfoods_*, you have wasted opportunities throughout the site. Anyone with a basic SEO background should be able to pick out page by page and show you missed opportunities (but would have nothing to do with the dramatic drop) The directory structure you are highlighting as good, is what I am highlighting as bad, it does not align with queries, it aligns with your own encyclopedic concept of data organization ala journal websites
A hint I would make is that you seem to drop the categories in your breadcrumbs/visible architecture from the page urls in favor of shorter urls. I never would have done that myself. /supplements/pyritinol/ should be in /cognitive-function/ or even better /cognitive-function-brain-health/
The backlink profile is problematic
I am not pointing fingers, just agreeing with a previous commenter, it is not an unusual backlink profile, it looks exactly like what my own would have looked like 8 years ago on hastily made affiliate sites that could generate 5 figures a month...in there first months (those days are gone), it just does not follow what the average "natural" site looks like.
As an authority site as you rightly pointed out, crap sites will link to you to mask their crapness, but why is the volume of off page anchors so perfectly matched to exactly what "you" would it need it to be> That would be a very sophisticated attack against you
I suspect your user testing was for an intelligent crowd or done by hacks, but usability is a legit platform - how big was the sample?
You will be moving up the ranks for "Adrafinil" shortly, for that term, Look at your search competition for the term, how do you stand out?
I cant believe i am saying this, but there is such a thing as too much interlinking and excess outbound links.
You just experienced the horror of google's nonsense. your site is far superior to the sites currently earning better positions - both in quality and traditional metrics we have all bee chatting about - you got hosed... so why do you seem to have such an organic focused strategy?
One post on Facebook a day? A cover image that is not optimized for mobile, little use of video content (you have tons of it in google's index)
You might not have purchased links ..would Sol? Lots of references to examine.com and it's rise to 7 figures in the entrepreneur/marketing/growth blogs - exactly the space full of people that do this type of quick and dirty link building.
Just wanted to try and answer your response, I realize this is a very stressful time and general jabs arent helpful, so was pecking out the most useful response I could on a phone ...and other than possibly the cloudflare option, nothing should be an immediate fix, but if your going to be digging into recovery
1. Open up new channels - minimize google reliance
2. Social space is perfect for supplements, get a social team
3. Find a middle ground between minimalism and "popular science" to make your site more attractive to a larger audience.
4. Try some actual optimization around queries instead of building around a sterile encyclopedia directory
5. Bribe a Googler
6. If all else fails, even the playing field and pay blackhatters to fill your crappy competition with unnatural backlink profiles, because if you didnt do it, someone did it to you, and they had money and a reason and Google is seemingly not following their own rules in how your being assessed
7. Look at the hubpages example - the site deserved it's destruction, but watch the desperation and poor decisions made trying to "fix" it for Google and the complete lack of feedback from Google they ever managed to get
Hopefully, Sullivans comment holds true and the algo gets tweaked just right to restore you to where you belong - and the tiny list of concerns I pecked out becomes meaningless for you.