The first, and main, problem I have with online ONLY training is you that you don't get an accurate sense of how they feel when rolling; how effective their gripping is, how active/responsive their hips are, where their base is centered, how smooth the transition is, how they react to adversity, their timing.. there's so many things that you can't get even close to the full scope of without hands-on drilling and rolling. So for example you might watch someone and see that a grip is in the wrong place, but a grip can be in the right place and still be ineffective to the purpose it's supposed to serve, which both the student and teacher are likely to miss unless the student rolls against someone competent while the teacher watches. Two white belts who have never rolled before are incapable of providing decent feedback. The second big problem I have with it is you have people repping incredibly imperfect reps without a teacher there correcting issues. You're drilling bad technique into your body, and the longer you do that, the longer it takes to unlearn it.