What he means is, if you just want to "do" the form, just complete the choreography, then you haven't learned anything. I do not dispute that one can use a video to mimick movement. You can learn the choreography and even make it look reasonably similar to the video if you work hard at it. But you haven't learned a thing, other than mimickry because you don't really understand what you are doing. This is what Sifu means when he says that every single movement must be done correctly. Getting thru the choreography in and of itself doesn't matter. Every movement within the form is teaching some very specific skills and you don't tap into those lessons by simply mimicking the choreography. You need very competent instruction to get those lessons. Telling your students "go ahead with this video and take a crack at it.." is doing them a disservice because you are really teaching them that mimickry is all that matters. Step here, punch here, block, whatever. But what are you really doing with that step, that punch, that block? Where is energy and power coming from? How are you using your stances, your footwork? A punch is not the same as every punch, nor block, nor step. There are different ways to do them, if you don't know the difference you won't even know what you are looking at.
I don't know TKD, maybe choreography is really what TKD forms are all about and there's nothing more to it. All I can do is speak for what I study, and the stuff that I do is much more than that.
Maybe our perspectives with our different systems just do not allow us to see eye to eye on this. That's fine. Like I said, I won't try to tell you that you cannot do this, that would be silly. I'm not your dad, I don't have any authority over you. But in the context of this discussion, I'll say very clearly that I absolutely do not believe it's a good idea to teach in this way.