Problem solving is about finding solutions to the road blocks one encounters along the road of life.
Blogs are really basically just a public dairy or journal of ones activities. Should it be any wonder then that Google expects a blog to be active? In a blog, new content is created with the publishing of new posts. New blogs should be publishing a new post every couple of days. One new post a week is sustainable for established blogs. But once a month updates signals a dying blog to Google.
To promote rational discussions of how to resolve a SEO problem with Google. The best place to start is by classifying the current status of your website.
The first step in the problem solving process is to correctly classify what your problem is.
SEOs that make a W3C Validation claim are just trolls trying to scam you into spending your time making worthless busywork changes to your website. Or, worst yet trying to scam you into purchasing their expensive SEO services.