Things change...Or do they?
I have been writing HTML since about 1998. When I started we used tables almost exclusively and you never closed the tags to save bandwidth. You injected a ton of keywords into content to get the search engines to notice your website and get yourself a higher ranking.
I'm not completely out of touch with HTML but I was baffled by the test on Linkedin. I'm not defending myself. I hadn't seen much of the criteria in my recent professional life however, I would argue that like semantic HTML much of what they presented isn't used in the real world, at all. The test almost exclusively revolved around displaying media and meta data. I have learned over many years that search engines aren't really concerned with the meta data as such... they "might" use it if it's available. It's like schema.org data. I used to spend a lot of time on that data structure to give websites information about the content on the site. Then months later I would run a search on the specific data and found nothing but still I would find the content using the context of the data in the surrounding page.
When Google started, the idea was that the web was effectively a popularity contest. Most of the search engines were tallying keywords and giving them weight whereas Google was more interested in who was going to your website. This hasn't really changed, if anything it makes more sense today than back then.
HAHAHAHA! I have wildly digressed from my original point that what is important about HTML is if the page renders quickly and consistently on all devices....That's what is important.
Symantec structure and meta data are not really important.