It appears that the reason this page from a little-known website is able to rank amongst the bigger players is that the content itself is more focussed. It talks about how to name images for SEO, whereas most of the other pages are more general guides to image SEO—which all presumably mention the importance of naming images correctly, amongst other things.
Meh, I disagree with your theory about using less tags. You should use all 500 characters for optimal results. There is no proof that likes/dislikes does anything to the SEO. I’m sure that is more for the content makers info and viewers warning. The description can be up to 5000 characters. Best to post your other video links. You have no proof of anything, noone does, we can only guess how youtube seo works..
One of my favorite ways to give content a boost is to run ads on Facebook targeting people with interests that are relevant to the content. It’s fairly low cost since you are offering a free piece of content. By targeting people with relevant interests to your content, you drive the right people to the content and into the top of your funnel. And if your content resonates with them, they’ll share, link, and engage with the content in ways that will help Google see its value.