I've had to do this for my two most recent jobs. I focused almost 0 on the formatting of the presentation and put all my energy into discussing my ideas and process (they normally tell you only to spend a few hours on the project, so I did).
The hiring managers had already seen my portfolio and past work at that point, so my goal was to really showcase how I think about content strategy as a whole (kind of regardless of the assignment) and how passionate I am about it—as that's what they likely want from a lead role.
So I talked about my process for writing the blog itself, but also kw research, likely customer pain points/jobs to be done we need to cover, how I might do research or find collaborators, other blog ideas I had when doing the exercise, distribution tactics for the blog/who might promote it, ways it could be reformatted, etc.
That let them see I was a holistic thinker and not just a good blog writer.