There is no reason not to do both, actually. Either can serve as the basis for creating the other.
However, if you do only one, you will leave out a fraction of your audience. People with vision impairment may prefer your videos, provided that the audio is good. This is a small group, of course.
But people with hearing impairment, a much larger group, including myself, won't get much from your videos and would much prefer written material. I don't really watch YouTube (or television, for that matter), unless the material is purely visual.
Moreover, it is difficult to annotate video presentations. You normally have to create a separate record and then it is hard to sync your notes with what is on the screen. Written material can much more easily be annotated.
But in the modern world, many people will prefer the videos, I suspect. But your planning for creating the videos and the audio script is also the same as the core of what you want in a blog.
So, Blog or Video? Yes!