I have to say that Yoast’s plugin is not absolute and Reading Ease score and other features can be misleading for adult sites. It can be a useful tool, you can leave it installed as it is, since basic configurations like adding sitemap, changing titles and metas can help but you should not use it for posts, videos.
Some of my posts that rank well on search engines got the red light from Yoast, so it is not the best indicator whether your content is optimized for SEO or not.
Just a common sense goes a long way, like not repeating the same keyword over and over again or adding the keyword twice in a one short sentence and et cetera.