a beginning student of the dance could get to grips with the fundamental principles and typical elementary movements of the dance in six months, instead of two years
I don't agree that the reason students can't do this is because of contradictory lessons or advice. I believe it's because so few teachers teach the most important fundamentals at the beginning at all, especially to large group classes.
To be fair, so few students are willing to take the time to focus on that stuff in the beginning.
I was lucky... my first teacher refused to teach anything BUT the important fundamentals to beginners. None of the fundamentals he taught me has ever been contradicted by another teacher, although it has been "corrected" by other students who didn't get taught anything but steps in their classes.