Without a teacher we would just learn the facts and when we went to the “real” world we would not know how to act and everyone would just feel a need to work alone as they had never worked with people which is where the teacher come in even in a class of one the teacher tells the student how to behave.
Ask any uni student where they most learn from. It's going to be online lectures.
And with development in A. I. It will not only be more efficient it will be a desperate need, Because some 70 million children are uneducated throughout the world and [that many] human teachers cannot be manufactured overnight