I have to say I think you're right. I think the advantage of a blog format is that it forces you to capture your thoughts in writing. So you have to challenge yourself.
But, having taught some in-person and synchronous online classes, the different points of view from students definitely force me to understand the topic at many levels.
One issue teaching might have that blogging doesn't is that it may be hard to find your audience, if it is a niche topic. For instance, I doubt that anyone would have signed up for a Cordova automation course (the topic of my ebook). But perhaps in a world of Udacity I'm incorrect.