Hi, “Cornerstone content” is made up term by Yoast marketing team. There is no mention of this term in Google Webmaster Guidelines or other reputable SEO sources.
Please realize a big chunk of “SEO” buzzwords is made up nonsense by people in the industry trying to make SEO more complicated than it is to sell more licences of their products.
From what I understand, Yoast is saying you should have a robust article with a lot of links going deeper in your site. The topic of the cornerstone content should be what you are expert in.
Look, this is frankly silly. Of course, you will write about a topic you are knowledgable about. Or a topic you enjoy. You will progressively do better and Google is getting better at picking up topics and categorizing a website.
Don’t let your creativity get limited by some stupid made-up rules that force you to write something you don’t want or need.
TSF is different, unlike other SEO plugins we ask you to only do what Google recommends, nothing else.
Let me end this with a quote by Greg Kogan:
The main principle to increasing search traffic is this: Help your target audience find what they need. That’s Google’s objective, too, so you’ll be working with Google instead of trying to trick it.
That’s it. Everything else you heard about SEO or were pitched by agencies is icing on the cake; it might help a bit, but first bake the cake.
I checked your website, you write about TV shows. This is a typical blog, write about stuff you enjoy. WordPress/TSF are designed to help Google understand your website. Use tags and categories, write something people want to read.
I understand you want to have a decent SEO, but everything starts with your content being enjoyable. Ranking a TV show blog is extremely hard, even if you dish out $1000/month for SEO tools and links.
I hope this sheds some light on the issue.
Cheers, Pierre.