With Google search engine results pages (SERPs), I think it will get worse over time as if it's not already bad.
From up to four ads at the top (they used to be on the right) to lists of "People Also Ask" questions, your #1 organic result really isn't #1 anymore. Think more like #5 or even #7. You need to scroll and scroll to actually see the famous first 10 natural search results.
I detail the problem with SEO rankings and include links to some other resources in a new Content Marketing Institute article, SEO Marketing Strategy: Tips for Success in 2018.
What's the bottom line? Don't view SEO as a one and done exercise. Analyze data to know when you can modify your SEO efforts and when it's best to create some new content.
If you can't get a #1 to be a real #1 anymore, you may as well land some other Top 10 results instead of settling for keyword rankings that don't accomplish anything.
Move up those #21 rankings and guard against losing search engine traffic because of the way Google stuffs all sorts of things with those SERPs.