When we live in the world of Star Trek TNG and have Holo Decks where we can interact with someone in 3 dimensions then it will work. Ever try learning martial arts from a book? Video? It's the same thing, I don't care how graet the practisioner is on the screen, if you are not in the room with the person you are not seeing all that's going on with the tech in all 3 dimentions. You might think you are copying exactly what the guy is doing in the picture from the front but maybe you back leg is all wrong, too bent, too straight, too wide, etc.
I'm sure we have all played sports on a team before. It's a huge difference playing around with your friend kicking a ball or swinging a racket/bat/hokey stick/golf club than the correct way your coach shows you (in a structured environment where performance matters), there is no difference in MA. It might look and feel right to you but still be all wrong and that's why you need a coach.