I don't think every blog needs a video. It depends on the search intent and the type of content you're publishing. For tutorials, product comparisons, or step-by-step guides, a video can definitely improve the user experience. On the other hand, for shorter informational posts or news updates, it's not always necessary.
Instead of worrying about the perfect length, I'd focus on making the video useful and engaging. In many cases, 2–5 minutes is enough to explain a topic without losing the viewer's attention. If the content answers the user's question clearly, people are more likely to stay regardless of whether the video is three minutes or ten.
I've tested both approaches, and in my experience, videos perform best on pages where users expect a visual explanation rather than just reading text.