I agree with some of what you said and I disagree with some. My disagreements are as follows:
Steemit's RATE of growth is much higher than Facebook at the moment in terms of numbers of users. I think a much better comparison would look at the rate of Facebook's early growth when it was first launched.
You don't have to have a grasp of blockchain. I agree that the site is not very user friendly, but neither was Facebook when it first started (remember that?), so I agree in terms of unoptimized design being a barrier for wide-scale adoption, but I don't see any need for the understanding of Blockchain to join Steemit...
Other than that, good analysis!
RE: Can Steemit Become as Popular as Facebook?