Seems like you're in a unique position to discover what the "Medic" update was really all about, as long as you're sure you didn't incur a link or over-optimization penalty. Though to really discover what the update targeted, you'd have to tweak one thing at a time and wait, which isn't a good idea.
Assuming there's no penalties involved, I'd go through and try:
Page level link profile (either add or dilute exact match anchors, get more & better links, etc.)
Content pruning (do you have a ton of low quality content with nearly zero SERP engagement?)
Is the entire site meant to rank this one keyword, or this just one page of many that took a hit? Either way, I'd apply the fixes and then ignore it beyond dripping out content once in a while, especially if it's your only site or main focus. These things can take a long time to improve, usually having to wait for Google to re-evaluate and still wait on the next update. You can have a new project rolling in the meantime instead of antagonizing over the one ranking.
We're slowly getting back to diversifying with SEO again. There was a long period where having one project made the most sense. I'd reckon having 2 or 3 makes the most sense now, across different industries entirely.
If and only if the first one is successful enough to fund it's own operations at scale and has left overs to fund another, while still providing you a healthy profit.
The caveat there being that you need to know when to let go of your first project if you have a dud on your hands, whether that's bad keyword research, Google simply hating it for some reason, or the entire algorithmic climate changing and altering a niche fundamentally (like many are experiencing in the YMYL niches) in a way that disqualifies you from playing.
I think that if you create a winner, you should focus on it with all of your bandwidth until you can begin offloading some effort onto service providers, employees, and/or virtual assistants. Once you get that down to the "four hour workweek" level, that's when you should start another. But having 2-3 or more projects at the start is really dooming yourself. The key is making sure you have a winner and not wasting years of opportunity pounding away at a lost cause, because time is the only resource you can't get back.
Well, Ryu I assume is talking about "authority sites".
I started with a "hobby niche" site, which I quickly figured out didn't have enough earning potential. I then pivoted to a small niche site, which quickly became earning (just 100-200 USD month), but I haven't touched the core content in months and it's still doing ok. Such sites I think "set and forget" can be fine, even to begin with. In my case, it's imperative for such a site, that it doesn't need much outreach and linkbuilding since that takes a lot of time.
I am in a similar position in which traffic dropped almost 80% (most of my keywords went from #1-3 to #7-10+). Earnings dropped from $10-20k to $3-4k
I did the following
1) Reworked content and deleted all content (around 25% of site) which were only tangentially related to my main niche. Disavowed all the low quality links and plan to buy only 3-5 links per month pointed to home and non-money page.
2)Started a new site in same niche with auction domain. Also upgraded some of my PBNs to money site. They have started ranking in page 3ish.
3)Bought an Amazon site from Flippa in a different niche with very few links and small earnings $500ish.
Now waiting for Google to settle a bit and trends emerge before doing serious link building.
Till then,I ll focus on content,design and $xxx branded links.