I think the point of Udacity, or at least why I did Udacity, is to get some kind of credential to get past HR gatekeepers (which did not work). I didn't do it to learn. I already taught myself Swift and iOS, and I'm sure I could have taught myself Android too, but I wanted some kind of credential, and I can't afford to get another degree.
You know all of those videos are optional? You can just skip the intermediary assignments if they are too easy, and go right to the final project in each section, which is the only part that is graded anyways. Also, the last project is a portfolio piece of your own design, so you can make it as hard as you want as long as it meets certain criteria.