You also do not need to linearly follow the topics/videos. You can take a few quizzes from some topic, notice you don't understand something completely yet and instead pick up more trigonometry instead.
I've worked through Khan academy in a way similar to what the author describes as a good flow, but then all within the Khan Academy platform. The platform even allows for discussions and questions.
To me the problem is much more that motivation or a destination is not something that Khan Academy will give you. Then again, so won't most teachers. I much preferred Khan Academy over most of my math teachers, but occasionally I've had teachers who helped me love a subject I barely knew beforehand.