Here is why they say content is king.
Google only cares about answering the users query the first time every time. Google will crawl your content and trying to gauge what your page is trying to explain. The longer the content, the better Google will feel it matches a particular search, based upon the keywords contained in the content. But this is only a part of how content helps you rank.
Google will test your content by moving you up the SERP to see how users respond. When this happens, we call it the "Goole Dance.", the same thing happens when you add backlinks. Your page will move up and down in the SERP at random for a while. When you are up in the SERP, Google is checking to see if your page is getting click-through and if users pogo stick on your site. Pogo sticking is when a user goes onto the page and then back to the SERP to click on another page in a short time. Here is where content becomes "King." Your content has to hold the user for as long as possible and answer their question. You do not want the user going back to the SERP and continue looking for an answer. To keep the user on the page and answer their attention content such as pictures, infographics, and video is essential.
If your content is not engaging and does not answer the searcher's question, you will be moved down in the SERP. While the length of content helps Google understand your page, in the end, it is about how the users interact with the content that will determine your final position in the SERP.