As someone who's taught writers of many levels--from graduate students to preteens--I agree with almost every word of this. And I love Coursera.

But from my perspective, online courses aren't enough. If you really want to improve, you need feedback IRL from a teacher or tutor who can sit down privately with you and give you honest feedback on your work. One drawback to online courses that is that all writers need constructive criticism, but a lot of teachers won't post negative feedback in any electronic form that could be easily shared. They'll tell you only in private what you most need to do to improve.